Telkom did not debit my account resulting to a hassle and negative reflection on my credit record

I took an iPhone contract with Telkom in October and we agreed that they will debit my account on the 29th of each month. At the end of October, they did not debit and I've always had money in my account with hope that they will debit. It is very sad that this very evening on Saturday, they disconnected my line, when I call they ask me to do a manual payment at the bank or one of the supermarkets, I am not allowed to do an eft, which is more convenient. When I asked to speak to a supervisor who can urgently assist me with my problem, as it is not my fault that they did not debit my account, the supervisors are not available and will only attend to me on Monday. This means my life comes to a stand still because Telkom did not debit my account, then proceed to make it my problem. I asked the lady if they can even debit now so I can have my line open, and she said I have to go and make a manual payment. I am wondering what was the point of sending my banking details and giving them permission to debit my account, a legal agreement, if they will further give me a hassle and negative reflection on my credit.