Undisclosed fees downward spiral

I have been using a Telkom mobile contract since 2018 mostly trouble free, renewed a number of times since then. The few times I had an issue I was able to speak to someone and my queries if any were resolved. What happened recently is my monthly bill increased slightly, and as a result my debit 'bounced' I made a direct payment and thought problem solved. I queried it when I got 'double debited' after paying only to find out that was not a double debit but a missed debit charge that costs as much as my account! Now for the last three months every time they try take more than is provided for, triggering the fee, missing the debit again and basically creating this chain of me having to pay double each month. I tried to speak to someone in the call center but all the options do is send you in an endless loop to force you to use the Whatsapp. The whatsapp cannot do anything so I go to the mall to the Telkom shop, at the Telkom shop they simply shrug their shoulders and say its the missed debit fee. I say I never knew about it, in seven years I have never come across it, they cannot show me where I signed for that either. I ask can I pay my bill here in the shop on the day of my debit, day one of the month and then carry on? I have paid bill every month even though the debits kept bouncing, I just need to get off this train please can you help, I have been your client all these years? No. I have to get the audio recording from 2018 where I took the deal over the phone and then perhaps they can look at it but without it, just pay. It was the 1st of the month, I say well then cancel my contract immediately (It was on a month to month anyway since January). I'm told it doesn't cost anything to change to prepaid, I say fine do it, I pay my last account and then we're square right? No, I still have to pay a missed debit fee again, and another one for the missed debit Yesterday, the day I cancel, day one of the month.