delivered the Opinion of the Court.
¶1 Glacier Kitchens, Inc., CR Weaver Trust, and the Estate of Grace Weaver (collectively “the Defendants”) appeal from the denial of their motion to set aside the default judgments issued against them in the Eleventh Judicial District Court, Flathead County. We reverse and remand.
BACKGROUND
¶2 On May 17, 2010, CR Weaver (Weaver), appearing pro se, filed a complaint in the Eleventh Judicial District Court, Flathead County, against Mountain West Bank (MWB) alleging breach of contract, unfair trade practices, and a violation of the implied covenant of good faith and fair dealing. MWB filed its answer and counterclaim for judicial foreclosure on June 4, 2010. MWB’s counterclaim included claims against both Weaver and the Defendants. On June 20, 2010, MWB attempted to serve the Defendants at the residence of Weaver by personally serving Weaver’s daughter Elizabeth Weaver (Elizabeth). Elizabeth bears no relationship to the Defendants, other than she is Weaver’s daughter. Elizabeth is not a registered agent or corporate officer of Glacier Kitchens, she is not a trustee of the CR Weaver Trust, and she is not a personal representative of the Estate of Grace Weaver.
¶3 On July 12, 2010, Weaver filed a pro se answer to MWB’s counterclaim as it related to him. The Defendants failed to file an answer or otherwise appear in the District Court. As a result, MWB applied for entries of default against the Defendants on July 26,2010. The. clerk entered defaults against the Defendants on July 28, 2010. On August 3, 2010, MWB applied for default judgments against the Defendants. The District Court issued default judgments on August 9, 2010.
¶4 On August 30, 2010, Weaver filed a pro se motion to set aside the judgments against the Defendants. In his motion, Weaver noted that Elizabeth was not legally qualified to accept service on behalf of the Defendants. MWB objected and argued that Weaver had failed to explain why Elizabeth was not authorized to accept service on behalf of the Defendants. MWB additionally contended that Weaver, as a non-attorney, could not appear on behalf of the Defendants. On November 1,2010, MWB filed a notice of issue with the District Court *278because the court had yet to issue a decision on the pending motions to set aside the default judgments. On January 12, 2011, MWB requested a hearing on the motions to set aside the default judgments. The District court did not respond to either of MWB’s requests.
¶5 On February 1, 2011, Weaver filed a second set of pro se motions seeking' to set aside the default judgments entered against the Defendants. These motions were again based on a lack of service, but this time Weaver cited M. R. Civ. P. 4D (2009), and included an affidavit from Elizabeth stating that she was not legally authorized to accept service on behalf of any of the Defendants. MWB objected on the grounds that the motions were duplicative of Weaver’s prior motions and that Weaver was still incapable of appearing on behalf of the Defendants.
¶6 Weaver then filed a pro se appeal with this Court on February 10, 2011, asserting that the default judgments should be overturned. See Order, Mountain West Bank v. Glacier Kitchens, Inc., DA 11-0083. We dismissed this appeal without prejudice due to the fact that Weaver, as a pro se appellant, was unable to bring an appeal on behalf of the Defendants.
¶7 F olio wing this Court’s dismissal, the Defendants obtained counsel, and on August 29, 2011, the Defendants, through counsel, made a motion to set aside the default judgments pursuant to M. R. Civ. P. 60(b) (2009). The Defendants argued that the default judgments were void because the District Court lacked personal jurisdiction over them due to MWB’s failure to properly serve the Defendants. MWB objected only on the basis that the motion was duplicative. The Defendants’ motion to set aside the default judgments was deemed denied pursuant to M. R. Civ. P. 60(c) (2009) when the District Court failed to rule on them within 60 days. It is from this denial that the Defendants appeal. ¶8 We restate the issue on appeal as follows:
¶9 Did the District Court err when it denied the Defendants’ motion to set aside the default judgments pursuant to M. R. Civ. P. 60(b) (2009)?
STANDARD OF REVIEW
¶10 We disfavor default judgments because of our policy that cases are to be tried on the merits. Mont. Prof. Sports v. Natl. Indoor Football League, 2008 MT 98, ¶ 21, 342 Mont. 292, 180 P.3d 1142. We review a district court’s decision to deny a motion to set aside a default judgment for only a slight abuse of discretion. Mont. Prof. Sports, ¶ 21.
*279DISCUSSION
¶11 The Defendants argue the default judgments entered against them are void because the Defendants were never properly served pursuant to M. R. Civ. P. 4D (2009). MWB argues that the Defendants’ motion to set aside the judgments was not timely, the claims are res judicata, and the Defendants were properly served.
¶12 MWB’s first argument regarding the timeliness of the Defendants’ third set of motions is itself not timely. At the District Court, MWB had the opportunity to object to the Defendants’ motions to set aside the default judgments on the basis of timeliness on three separate occasions and failed to do so. Weaver first attempted to set aside the default judgments less than thirty days after the District Court issued the default judgments. MWB argued only the merits of the motions and that Weaver could not represent the Defendants. Weaver next attempted to set aside the default judgments less than thirty days after MWB requested a hearing on the pending motions. In response, MWB argued on the merits of the motions, that the motions were duplicative, and that Weaver could not represent the Defendants. Weaver’s third set of motions was filed shortly after he obtained counsel. MWB relied on the same merit based arguments, and that the motions were duplicative. In total, MWB was presented with three variations of the Defendants’ motions to set aside the default judgments, yet MWB failed to seize these opportunities and argue timeliness. Instead, MWB presents it for the first time on appeal.
¶13 Our rule with regard to arguments presented for the first time on appeal is well established. We will generally not address either an issue raised for the first time on appeal or a party’s change in legal theory. Becker v. Rosebud Operating Servs., 2008 MT 285, ¶ 17, 345 Mont. 368, 191 P.3d 435 (citing Day v. Payne, 280 Mont. 273, 276, 929 P.2d 864, 866 (1996)). There is no evidence that MWB ever raised the issue of timeliness regarding the Defendants’ M. R. Civ. P. 60(b) (2009) motion in the District Court. Because it would be “fundamentally unfair to fault the trial court for failing to rule correctly on an issue it was never given the opportunity to consider,” we will not now consider MWB’s timeliness argument. See Day, 280 Mont. at 276-77, 929 P.2d at 866.
¶14 MWB next contends that the Defendants’ motion to set aside the default judgments is res judicata because it is the Defendants’ third set of motions on the same issue. The doctrine of res judicata bars re-litigation of a claim that a party has already had the opportunity to litigate. Touris v. Flathead County, 2011 MT 165, ¶ 12, 361 Mont. 172, *280258 P.3d 1. Res judicata, however, only applies once a final judgment on the merits has been entered in an earlier action. Touris, ¶ 13 (emphasis added). In order to have a preclusive effect, a final judgment must be a valid judgment because an invalid judgment is no judgment at all. See Mason v. Genisco Tech. Corp., 960 F.2d 849, 851 (9th Cir. 1991) (“A person is not bound by a judgment in a litigation to which he or she has not been made a party by service of process. Hence, if Genisco failed to serve Mason properly in the earlier action, the default judgment is void and has no res judicata effect in this action.”) Accordingly, only a valid judgment may be the basis of the application of res judicata. James Wm. Moore, Moore’s Federal Practice, Vol. 18, § 131.30(l)(a) (3d ed., Matthew Bender 2012). Because we find the default judgments void, as discussed below, the doctrine of res judicata does not bar the Defendants’ motion.
¶15 We now turn to the Defendants’ argument that the default judgments are void because service was not properly made pursuant to M. R. Civ. P. 4D (2009). The Defendants argue that service of process was flawed and, therefore, the District Court acquired no jurisdiction over the Defendants thereby rendering the default judgments at issue void. MWB argues that the default judgments are valid because the Defendants were properly served when Elizabeth accepted service on their behalf and the Defendants were put on notice of the pending lawsuit when Elizabeth accepted service.
¶16 A district court may relieve a party from a final judgment if that judgment is void. M. R. Civ. P. 60(b) (2009). A judgment is void if service of process is flawed due to the fact that the district court never acquired personal jurisdiction over the party. Semenza v. Kniss, 2005 MT 268, ¶ 18, 329 Mont. 115, 122 P.3d 1203. Service is flawed if the mandates of M. R. Civ. P. 4D (2009) are not strictly followed, “even where a defendant has actual notice of the summons and complaint; knowledge of the action is not a substitute for valid service.” Fonk v. Ulsher, 260 Mont. 379, 383, 860 P.2d 145, 147 (1993); See In re Marriage of Blaskovich, 249 Mont. 248, 250, 815 P.2d 581, 582 (1991). Thus, if the Defendants were not served in accordance with the dictates of M. R. Civ. P. 4D (2009), then the default judgment is void. See Semenza, ¶ 19.
¶17 In the case at bar, the Defendants comprise a corporation, a trust, and an estate, and they must be served as such. A corporation may be served by delivering a copy of the summons and the complaint to an officer, a director, a manager, a member of a member-managed limited liability company, a superintendent, a managing agent, a general *281agent, or a partner. M. R. Civ. P. 4D(2)(e) (2009). A trust must be served by delivering a copy of the summons and complaint to any of the trustees. M. R. Civ. P. 4D(2)(i) (2009). An estate must be served by delivering a copy of the summons and complaint to the personal representative. M. R. Civ. P. 4D(2)(i) (2009).
¶18 Here, as in Semenza, the default judgment is void because the Defendants were not properly served as strictly mandated by M. R. Civ. P. 4(D) (2009). Elizabeth could not accept service on behalf of Glacier Kitchens, a corporation, because she was not “an officer, a director, a manager, a member of a member-managed limited liability company, a superintendent, a managing agent, a general agent, or a partner” of Glacier Kitchens. Elizabeth likewise could not accept service on behalf of the CR Weaver Trust because she was not a trustee. Elizabeth also could not accept service on behalf of the Estate of Grace Weaver because Elizabeth is not a personal representative of the estate. We thus conclude that service of process was never accomplished on the Defendants, and as a result, the District Court never acquired personal jurisdiction over the Defendants. Consequently, the default judgments against the Defendants were void ab initio, and the District Court, therefore, erred when it failed to set aside the default judgments issued against the Defendants.
CONCLUSION
¶19 For the reasons stated above, we reverse the District Court’s denial of the Defendants’ motion to set aside the default judgments and remand this matter for further proceedings consistent with this Opinion.
CHIEF JUSTICE McGRATH, JUSTICES COTTER and MORRIS concur.