This is a DV- You are not required to submit ANY documentation
They did not say it was past your 30 day window- so IMO- They are in violation o FDCPA
They ALSO acknowledged to be i receipt of your first DC-
(D)Submitting a notice of dispute- A consumer who seeks to dispute the accuracy of information shall provide a dispute notice directly to suchperson at the address specified by the person for such notices that--
(i) identifies the specific information that is being disputed;
(ii) explains the basis for the dispute; and
(iii) includes all supporting documentation required by the furnisher to substantiate the basis of the dispute.