Telkom's Billing bungle becomes my problem

I have a 24 month data contract with Telkom, for which they debit my account on a monthly basis. That has been the case for a long time now. I found myself suddenly without internet, to find that Telkom had decided to stop debiting my account a few months ago. No reason whatsoever. There was money in the account, and money for the months after that. This has now resulted in a bill of close to a grand in arrears, for which Telkom has suspended my account until I make payment. Why is this my problem if you have decided to stop debiting my account? If you hadn't done so, there would be no arrears. It is not my responsibility to make sure you debit my account, as the contract signed kinda stipulates that you will do so. This is pathetic. The call center agent's response was even worse. They are not willing to even come back to me with an answer as to whether they are going to make it right, if it is found that this is actually their fault