The CFPB says you have the right to dispute credit report errors, and fixing one generally means contacting both the credit reporting company and the company that provided the information. If you suspect identity theft, it points to IdentityTheft.gov.
Start with Experian, Equifax or TransUnion. Explain in writing what is wrong and why, and include supporting documents. A mailed letter should include your name, address and phone number, the report confirmation number if available, each error with its account number, a clear explanation, a request to remove or correct it, a copy of the report section with disputed items marked, and copies, not originals, of supporting documents. You may send it by certified mail with a return receipt. TransUnion takes phone disputes at (800) 916-8800.
The credit reporting company must investigate, forward your dispute and documents to the company that supplied the information, and report results back. It need not investigate disputes it reasonably decides are frivolous or irrelevant, but it must send you a notice explaining why within five business days of that decision.
Then dispute with the furnisher, such as your bank, landlord or card issuer, in writing by certified mail. The CFPB says furnishers generally must investigate and respond within 30 days of receiving the dispute. Keep copies of all letters.