Perrie, Buker, Stagg & Jones, P.C., a law firm, sued its client John Schluter to recover unpaid attorney fees. Schluter complained the amount of work performed was excessive and in part unauthorized. The trial court granted the firm summary judgment. The issue is whether the evidence is undisputed that the work billed for fell within the parameters of the parties’ agreement.
Schluter and Richard W. Jones, a principal in the firm, executed a letter agreement on the firm’s letterhead authorizing Jones to prepare the documents necessary for a private placement offering of limited partnership interests in a new dining and entertainment club. It stated: “The legal work necessary for the proposed offering will entail the preparation of a private placement memorandum, preparation of subscription documents, preparation of appropriate regulatory filings, preparation of amendment of limited partnership agreement, partnership organization and cleanup work and other collateral work.” Schluter agreed to pay invoices which would consist of expenses and fees calculated on an hourly basis for the services performed. The agreement set forth an hourly rate of $140 for Jones’ time. It stated as “estimates” that the project would take about two weeks and that the fees would range from $12,000 to $18,000. The agreement explained that the estimates were based on Jones’ experience in matters of the same nature, did not constitute any guarantee, and could be greater. Within four weeks Jones, with the assistance of a firm associate, prepared and delivered the documents to Schluter’s son and business partner, Douglas Schluter, who had the documents copied and bound. The firm submitted invoices to Schluter which amounted to $17,579.50 in fees and $1,559.94 in expenses. Schluter refused to pay more than $10,203.85. The firm brought suit in two counts, open account/breach of contract and quantum meruit, and sought in addition attorney fees for bringing the suit. The court granted summary judgment on the open account/breach of contract claim.
1. “An action on open account is a simplified pleading procedure where a party can recover what he was justly and equitably entitled to without regard to a special agreement to pay such amount for goods or services as they were reasonably worth when there exists no dispute as to the amount due or the goods or services received. An action on open account may be brought for materials furnished and work performed. However, if there is a dispute as to assent to the services or to acceptance of the work done or as to what work was to be performed and the cost, then an action on open account is not a proper procedure. A suit on account must be based either on an *777express or an implied contract.”1
Schluter has challenged the firm’s billings, which takes the case outside the simplified parameters of an action on open account. The firm’s claim must proceed as a breach of contract action.
Schluter urges that factual disputes exist as to four matters. First,' he claims the firm agreed to keep the fees and expenses in the low end of the range identified in the agreement. This contradicts the written agreement which provides Jones could not promise the fees would even stay within the estimated range. Similarly, Schluter’s argument that the parties agreed the project would take no longer than two weeks is inconsistent with the written terms stating the two-week figure was only an estimate and the project might take longer.
But oral understandings cannot be admitted to contradict written terms.2 “Well-established Georgia law provides that matters outside a contract cannot be used to vary or explain the unambiguous terms of an agreement. While, generally, an ambiguity in a contract may be explained by parol evidence, parol evidence is inadmissible to add to, take from or vary a written contract. (OCGA §§ 13-2-2 (1); 24-6-1; and 24-6-2.) Where the contract is complete on its face and the evidence offered to explain the ambiguity contradicts the terms of the written instrument, it should not be admitted. Moreover, parol evidence of a mere understanding arrived at subsequent to the contract as to the meaning of the prior writing is inadmissible.”3
Second, Schluter claims the tax research and analysis exhibited in the documents “was neither necessary nor appropriate” and the extent of it was unauthorized. Schluter’s personal testimony that the detailed tax analysis was excessive legal work is not competent evidence for the reason that he lacks a law degree. The law presumes that lawyers perform legal services in an ordinarily skillful manner.4 “This presumption remains with the attorney until the presumption is rebutted by expert legal testimony; otherwise, the grant of a summary judgment in favor of the attorney is proper. Should this presumption be rebutted by expert legal testimony there is presented for the jury a question of fact.”5 Findley v. Davis6 applied this presumption where the client claimed the fees exceeded the value of the ser*778vices rendered and expenses incurred.
Aside from this presumption, Schluter’s personal opinion does not provide a legal evidentiary basis for his defense that the legal tax work was inflated. To prove such requires the opinion of a legal expert in the field. The firm submitted the affidavit of Jones, who was qualified to give an opinion because he had practiced law for 14 years in connection with over 60 similar securities offerings. Because it was his opinion that the work was reasonable and necessary, Schluter’s failure to present contrary competent testimony dissolved this defense.7
Schluter’s other two allegations of factual dispute have merit. First, he testified that three meetings with “Mr. Schluter” appearing on the invoices did not take place, and as to two of them, he was out of town. In response, the firm on the day before the hearing filed an unsworn “affidavit” from Jones, who sought to explain that the invoiced meetings were with Schluter’s son, Douglas Schluter. Because unsworn statements are not regarded as affidavits and do not constitute competent evidence to support a motion for summary judgment,8 and because the document was filed later,9 the trial court correctly struck and did not consider it. Moreover, two of the disputed billing entries on successive days each refer to a meeting with “Mr. Schluter,” revision of a partnership agreement, conference call with “Mr. Schluter,” meeting with “Douglas Schluter,” and work on a memorandum. This would imply that there were two different meetings each day with two different individuals. Because Schluter testified he attended no such meetings, a disputed issue of fact exists.
Second, Schluter points to hours worked by “CVS,” apparently an associate at the firm, and claims he never authorized the firm to allow anyone other that Jones to work on the matter. The agreement is ambiguous on this issue. It is on the firm’s letterhead but is signed by Jones without any express designation that he is signing on behalf of the firm. The agreement refers to the billing policies of the firm but states “I will strive to complete the preparation of the documents necessary to effect your proposed offering as expeditiously as possible at a fair and reasonable cost to you.” The agreement refers only to Jones’ hourly rate. Ambiguities in agreements are construed against the drafter.10 In light of Schluter’s testimony that he did not intend to authorize anyone besides Jones to work on the matter, the fact is disputed. This obviates a need to determine whether evidence from *779“CVS” was necessary to prove the work attributed to her. Her affidavit was struck as being filed too late.
The disputed issues of fact precluded summary judgment on Count 1, and thus, the granting of it was error.
2. There is no ruling to review in connection with Schluter’s enumeration as error the grant of summary judgment on Count 2, the quantum meruit claim. The firm moved for summary judgment only on Count 1, the claim on an account, and the trial court awarded summary judgment on that count alone.
Judgment reversed.
McMurray, P. J., concurs specially. Smith, J, concurs in the judgment only.(Citations omitted.) Watson v. Sierra Contracting Corp., 226 Ga. App. 21, 27 (b) (485 SE2d 563) (1997) (physical precedent).
See Loveless v. Sun Steel, 206 Ga. App. 247, 248-249 (1) (424 SE2d 887) (1992).
(Citations and.punctuation omitted.) Choice Hotels Intl. v. Ocmulgee Fields, 222 Ga. App. 185, 186-187 (1) (474 SE2d 56) (1996).
Roberts v. Langdale, 185 Ga. App. 122, 123 (1) (363 SE2d 591) (1987).
Hughes v. Malone, 146 Ga. App. 341, 349 (247 SE2d 107) (1978); see Findley v. Davis, 202 Ga. App. 332, 337 (2) (b) (414 SE2d 317) (1991), rev’d on other grounds, 262 Ga. 612 (422 SE2d 859) (1992); Rose v. Rollins, 167 Ga. App. 469, 471 (2) (306 SE2d 724) (1983).
202 Ga. App. 332.
See generally Howard v. Walker, 242 Ga. 406, 408 (249 SE2d 45) (1978); Findley v. Davis, supra, 202 Ga. App. at 337 (2) (b); Graves v. Jones, 184 Ga. App. 128, 129-130 (1) (361 SE2d 19) (1987).
See Huiet v. Schwob Mfg. Co., 196 Ga. 855, 859 (2) (27 SE2d 743) (1943); Barrett v. Wharton, 196 Ga. App. 688, 689 (396 SE2d 603) (1990).
See Corry v. Robinson, 207 Ga. App. 167, 169-170 (2) (427 SE2d 507) (1993).
Gram Corp. v. Wilkinson, 210 Ga. App. 680 (1) (437 SE2d 341) (1993).