The DV letter you sent was timely correct? If so I would send them the proof you have that they signed for the DV letter and remind them of FDCPA 809; particulary 5(b).
I would also tell them you intend to sue if they continue to try to collect without first answering your DV request. There is no time limit for them to respond to a DV but as 5(b) indicates they cannot keep trying to collect until and if they do validate.
809. Validation of debts
(a) Within five days after the initial communication with a consumer in connection with the collection of any debt, a debt collector shall, unless the following information is contained in the initial communication or the consumer has paid the debt, send the consumer a written notice containing --
(1) the amount of the debt;
(2) the name of the creditor to whom the debt is owed;
(3) a statement that unless the consumer, within thirty days after receipt of the notice, disputes the validity of the debt, or any portion thereof, the debt will be assumed to be valid by the debt collector;
(4) a statement that if the consumer notifies the debt collector in writing within the thirty-day period that the debt, or any portion thereof, is disputed, the debt collector will obtain verification of the debt or a copy of a judgment against the consumer and a copy of such verification or judgment will be mailed to the consumer by the debt collector; and
(5) a statement that, upon the consumer's written request within the thirty-day period, the debt collector will provide the consumer with the name and address of the original creditor, if different from the current creditor.
(b) If the consumer notifies the debt collector in writing within the thirty-day period described in subsection (a) that the debt, or any portion thereof, is disputed, or that the consumer requests the name and address of the original creditor, the debt collector shall cease collection of the debt, or any disputed portion thereof, until the debt collector obtains verification of the debt or any copy of a judgment, or the name and address of the original creditor, and a copy of such verification or judgment, or name and address of the original creditor, is mailed to the consumer by the debt collector.
(c) The failure of a consumer to dispute the validity of a debt under this section may not be construed by any court as an admission of liability by the consumer.
Edited for a typo.
