When I dropped DirecTV, I only had to mail in the card in the receiver, did not return the receiver.
If the auto-pay is initiated by DirecTV, I believe they will have to stop it. It is taken out of the bank by DirecTV instead of the bank sending payment at your request.
For this reason, I will not use it. I use bill pay service and let them send me an invoice by email and I create the payment.
Good luck. Hope you get it resolved with DirecTV.