DIRECTV— Notice of Dispute (no response)

I submitted a Notice of Dispute in accordance with the terms of my agreement, and mailed it to DIRECTV LLC, Consumer Arbitration Demand, P.O. Box 915, El Segundo, CA, 90245 as set out in the instructions.  I have not heard anything in more than 30 days.  What do you suggest I do next?  File for arbitration?