If after you ask a CRA to investigate a debt and they come back and verify it, what else can you do if you are pretty sure that there is nothing to substantiate the verification?
Send a validation letter to whoever the creditor or collection agency is. Do a search here for "validation letter"
Ask that they re-investigate it. Wait a period (30 days) and try again. Investigate it for another reason.
Original creditors don't have to "validate", only CAs. Experian would not reinvestigate mine after about three previous disputes regardless of the reason. If you know for sure that the creditor is verifying incorrect information, write a letter to the creditor through Planetfeedback. If no response in about 2 weeks or so, file a complaint with BBB and maybe even FTC.