Mtn South Africa

I was having a contract with mtn, which i fully paid in 24 months. Mtn decided to renewed the contract. I contact the several times and they said i should pay R600 cancellation fee which i did at the mtn store. Mtn decided to turn the R600 into advance payment without my knowledge. After 2 months the deducted R545 which it..i contacted the promised to close it. Today i received their message which state that they will blacklisted me if i don't pay the account. I've all the receipt and recording of the agents i spoke with... Mtn can you close the account asap for i will report it,if not removed within 24hrs