Based on that, there really is no violation, unless you live in Texas where all DV's are timely. They did not have to respond to your DV in any way, nor cease collection activity, and unfortunately, their response was to send this thru arbitration. I would start doing some research on refusal of arbitration. Depending on when this account went delinquent, there might not have been a BMA clause in effect at the time. When was the account opened and when did it go delinquent? Who is the OC?
Also, PM me and I can get you a link to some good refusal of arbitration cases