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Was it personal identifier information, and thus they could not assure that you are the named consumer?
Can you reproduce a copy of their specific statement?
Then file your dispute via mail.
You would mail the dispute to the CRA, and include proof of your identity along with your identification of what is inaccurate in their reporting, and any accompanying documentation that supports your assertion of inaccuracy.
See FCRA 611(a).
You should call them and do their ID verification process. I had to do this and it removed the issue with whatever info wasn't matching when I tried.