UNAUTHORISED DEBIT ORDER BY MTN

Good Evening, My name is Nthabiseng Cele ID number ***. I had contract with MTN SA for almost 10 years now. Since i had a contacts with them my debit order was on the 20th of every month when i get paid. I upgrated my phone on the 12th of August 2020 and everything went well and i was happy with the service, and before the 20th of August 2020 i called MTN and spoke to the lady Nombulelo and she advised that my debit order for august will be the previous installment. On September the installment will be R490 per month. Only to found out that today i received an SMS from my bank to advise that the debit order for the amount of R490.13 from MTN run today on the 8th of September 2020. I was so ****ed off and angry because i am well aware that there is no money on my account because all my debit orders goes on the 20th every month. i dont have any debit order that run on the 8th, i called them and spoke to a guy Lizalethu who explained that the debit order run this month because MTN is running a compaign to my something i dont know what is that and also said they send sms regarding that and when they migrate things didnt go well and the debit order didnt run so that is why they debited my account on today. i asked to speak to the manager. He called Songeziwe and he esplained the same thing that when they run the compaign the debit orders didnt go through hence why they only debited now. So my ****en question is that how is my fault that they didnt debit my account and now my ****en profile is messed because ive never had a reversed debit order in my account at mtn and at the bank. The manager said she will lock a query with the reversal because from their side it charge R11 rand when i provide them with proof of reversal. I ****en asked that what about the bank because they are going to charge me R115 not sure if its still the same amount because there is no money in my account. He said he doesnt know the only thing he knows is that they can reverse the charge from their side not the bank one. ive been a loyal customer to the MTN for the past ****en 10 years if not more, and ive never skipped any debit order and now they are messing up my payment profile and causing reversal on debit order that they are not authorised to do. who gave them permission to debit my account on the 8th because i gave permission for the 20th every month and even the manager confirms that the debit order details are not amended they are still the same so please can someone tell me why and i am not ****en liable for the R115 for the reversal from the bank, MTN will have to pay for the unpaid debit order from my account urgently or cancel the dam contract urgently.