Actually, the way they work is "x company told me y person has <this account> with <these details>". For non-celebrities, it is only defamation if it amounts to

Actually, the way they work is "x company told me y person has <this account> with <these details>". For non-celebrities, it is only defamation if it amounts to at least negligence in verifying these facts - i.e. negligent only if they have reasonable knowledge to believe the information is false. When you report to the bureaus that an account is fraudulent, that is effectively giving them notice that the account in question is not actually yours, and by removing it from your report, it's relieving them of the liability of spreading such defaming information in the future.