MTN billing when contract has long ended

My cellphone contract with MTN ended in July 2022 which I then called them to cancel. Since then it has been a constant struggle trying to cancel the extra charges they keep billing me for😡. When I call, I get transfered to every department and everyone claiming the system did not log my cancellation. I then get asked to call back on a specific date and when I do, again I get given the runaround. It's so frustrating and till this day I get statements that I owe them. I wrote and called them telling them how this affected my credit score as these charges are not being debited, which was the case with my contract (further showing it has ended) , the legal department which I was told to email did not respond. The worst service provider ever!