Terrible service at Telkom

I have 4 different contracts with telkom, all paid monthly via debit order. Never any issues with payments. However, around July, my debit went off as usual the morning. Late afternoon I received a text claiming that I would be penalized for non payment of my account. I went to the bank and drew a statement, clearly showing the debit did go of, but had then been reversed. I went to a telkom shop to ask what the issue was, I was advised that I was not the first customer to ask the same question that day. and that other customers had the same issues with debits being reversed. after that I went to Checkers and paid the amount owed in cash on my telkom account. now Telkom is still penalizing me with a huge fine for late payment. I am struggling to get this sorted out as one of the call center managers keep telling me that I must prove that it was an error on their side.....I provided a copy of my bank statement showing that I had sufficient funds, and that the debit reversed automatically I also sent a copy of the proof of payment I made that same day. and now they want me to go to my bank and ask them why it was reversed? I am being sent on a chicken chase for all the information they are asking for, however, they are not willing to look for issues on their side. Why should I be liable for such an astronomical fine if the issue laid with my service provider?