Debit order complaint

I hate Onair TV, I bought an explorer decoder last year in May, the consultant and I agreed that the debit order would go through every month on the 20th since the beginning they have been deducting twice a month, I'm so fed up with their services I feel like sending the decoder back as it is still not installed. Now all of a sudden I get a message from them telling me I'm in arrears, how is that possible when they deduct twice a month, I want nothing to do with the company anymore and when you call them to complain their lines are always busy.