Wrongfull debit order

Good day Once again a complaint about cell c. This time about accounts department. We have contracts with them for over 4 years now. Every month for the past 4 years we are paying our account with cell phone banking into cell c's bank account. This month they let us know on the one contract that they will cut the line because of short payment. After long struggle we found out than all of a sudden they set up a debit order (without my consend) for this month and now they want to charge us for the failed debit order????(This is the arrear amount all of a sudden) ***??? After all this time of paying into cell c's account. I will not be held responsible for this "failed debit order" charge!!! Please cell c wake up.