Failer to cancel my contract

I had a month to month contract with MTN which I closed on the 17th of August due to the fact that they stopped my connection which was already paid for without any communication from them. They haven't canceled my contract even though I went to the store to personally close it, it's still active and shows that it has an outstanding balance I have to pay and this is affecting my credit score as it is showing a missed payment. I went to the store to return the device and cancel the subscription on the 17th of August 2024, Shop1225 Mall of Africa, Magwa Crescent. I have signed forms that I canceled the subscription and returned your device. Cancel my subscription as agreed because I will not pay MTN any amount as they stopped my connection which was paid for with no communication from the service provider. Infact MTN owes me for the days I was without internet, a lot of inconvenience was caused.