A dispute sent straight to the company that reported the information is a direct dispute, and it is governed by Regulation V, 12 C.F.R. § 1022.43, together with the furnisher responsibilities in the Fair Credit Reporting Act. The rule requires a furnisher to conduct a reasonable investigation of a direct dispute relating to your liability for an account, the terms of the account, your performance or conduct on it — current payment status, high balance, the date or amount of a payment, the date the account was opened or closed — or other information on the account bearing on your creditworthiness. If the investigation shows the information was inaccurate, the furnisher must promptly notify every credit reporting company it sent that information to and provide the correction.
Two things determine whether your letter triggers that duty at all.
Where you send it. Regulation V requires a furnisher to investigate a direct dispute only if you send it to the address the furnisher provides on your consumer report, or an address it has clearly and conspicuously specified for direct disputes; if it has designated neither, any business address will do. A letter to a general customer-service address may simply be handled as correspondence. Use the dispute address printed on the current report or the one the company publishes for this purpose.
What you put in it. The rule expects enough information to identify the account, the specific information you are disputing with an explanation of the basis for the dispute, and the supporting documentation reasonably required to substantiate it — the rule itself gives examples: the relevant portion of your consumer report, a police report, a fraud or identity-theft affidavit, a court order, or account statements. A dispute that does not provide enough to investigate may be treated as frivolous or irrelevant, and so may one that is substantially the same as a dispute already resolved, unless you are supplying information the furnisher did not have before.