Send a letter via Certified Mail + Return Receipt to Experian stating:
I am requesting written validation of this alleged judgment against me. Provide the name of the court which issued this alleged judgment and the date that this occurred.
This letter has been sent via Certified Mail and is officially being time stamped. Refusal to validate will be officially documented.
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If this is not your judgement and Experian still refuses to remove it after sending this letter, then your only recourse is to sue for Fair Credit Reporting Act violations.