Billing issues, customer service

I have had direct TV for years and have always had auto draft to pay the bill.  Yesterday I received an email that my account had been cancelled due to non payment.  I called and your rep told me that the bank had return two payment attempts at the end of July.  I called my bank who advised that they had not and that the account had been drafted each month as usual.  I called your customer servie and all they could say was I had to pay a past due amount.  First of all, I have already paid in full.  Secondly, why was I not notified if Direct TV thought there was a problem before receiving the only email I got, which indicated the account had been closed (out of the blue)  Now apparently, my only recourse is to write a formal dispute and wait.  Any others suggestions to get this cleared up?