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I presume that you sent the debt collector a DV, and then they deleted their reported collection.
Deletion after a DV request does not mean the debt collector "could not validate." There is no period for or requirment to send validation after receipt of a DV.
If the DV was timely, then it imposes a cease collection bar, which remains in place until they choose to verify.
Lack of verification of the debt does not substantiate that the debt could not be verified.
The debt collector can choose to simply delete their reporting at any time.
In the case where the creditor terminates their assigned collection authority to reassign to another debt collector, which is apparently the posted scenario, then th first debt collector is required under CRA policy to delete their reporting collection.
That carries no implication that the debt could not be validated, and does not prevent the new debt collector from reporting their new collection.
The date of the new collection does not make the debt new. The debt collector must report the DOFD, which remains the same.
If the debt is not yours and you can make that assertion in a sworn statement before a law enforcement agency, neither the DV nor the dispute process is the proper procedure. You can file a police report and use the identity theft process under FCRA 605B to get the collection blocked from your credit report without any involvement of the debt collector in the process.