MTN ********ly ruins my credit record

My name is Thandaza Ngxongwana I had a contract with Mtn and all my life I have been with Mtn, my contract lapsed 26 November 2020 and I called to cancel but after that they still kept on debiting my account and I have been calling to ask them to cancel and stop debiting me monthly as I have canceled my contract, I then decided to reverse the debit orders since they refusing to stop debiting my account monthly because according to them I have not canceled the account and eventually after several calls and going to their branch someone decided to investigate and listened to a call where I canceled my contract and promised to go back to finance and fix my account so they can cancel my contract and refund me but no one ever did, I then got a shock of my life from lawyers that I have been handed over and black listed, this is now affecting my credit score and I cannot be approved for anything I am applying for, a house nor a car all because MTN still wants to bill me for a contract I no longer have and now I can't even cancel my second contract so now I'm incurring more costs for contracts that has expired, I no longer know what to do to clear my name and get a clearance letter and paid up letter so I can be able to clear my credit.