They are not cancelling my contract

Taking out a contract with MTN was the biggest mistake Of my life. I took out a cellphone contract with MTN in 2018 September, and I decided to pay it off last month (March) I told them I was to keep my number it must be migrated to prepaid, since the date of the cancellation of my contract I can’t receive calls on my phone, I tried to call them countless times. They tell me that they can’t see anything wrong but I still can’t receive calls. 2, second issue, I paid off my account and you still debited R1381 in my account for the contract that I paid off and mind you I was only paying R700 for my contract. I decided to reversed the money, 3 third issue- I received an SMS saying that my account was changed to cash billing and my account number is BA***,

Why do I still need to make cash payment for the account I paid off. Why is it so hard for you guys to cancel the contract that I paid off. Why are you still debiting my account. I don’t owe you guys anything. I paid every cent that was asked before cancelling my contract. Can you please, I beg, cancel my contract , stop debiting my account coz the next thing you’ll be telling me that I owe you guys whereas I don’t owe you a cent. This is going to affect my credit. And I don’t want that. Please I beg , cancel my contract and stop debiting my account. Why am I still on your billing payment. I don’t owe you anything