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A DV request imposes no requirment that the debt collector send any validation.
If you assert that their validation is inadequate, then you can advise them as such.
However, lack of validation is not per se a violation of FDCPA 809(b). It is simply the absence of validation.
If your DV was timely, then the result is that you are advising them that you consider them to still remain under a cease collection bar.
Violation of FDCPA 809(b) would then occur only if/when they resume collection activities without first providing adequate validation.
As stated in prior posts, FDCPA 809(b) does not mandate that they include documentary "proof" to support their statement of validation.
Since the post makes no reference to their having reported their collection, there is no basis for a dispute of accuracy of their reporting under the FCRA.
You can simply send an advisory letter informing them that you consider their response to be inadequate validation and wait.
Should they resume collection activities AND your DV request was timely, you can then initiate civil action for violation of the FDCPA and get the decision of a court as to the adequacy of their purported validation.