After so many queries with MTN, they have decided to suspend my lines stating I owe them

After so many queries with MTN, they have decided to suspend my lines stating I owe them. I don't owe them because they have confirmed with me in writing last month that I'm upfront with my account and I don't have to pay for September. They do debit into my account bank at any day without my knowledge. I have been querying this from May 2021 but with no luck. I'm frustrated as my credit profile went to bad due to this unauthorized debits. I don't know who can finally assist me as I don't know what to do with this problems created by them. If I had a choice I would have been cancelled my contract with them, but I can't because it's a new contract. I have been with MTN for more than 13years, however what they are doing to me it's now unacceptable. They are playing with my emotions knowing very well that I'm stuck with them for two years with this contract. But the time will come where I will leave them for GOOD. From loyal Unhappy customer