MTN contract

I have settled and closed my contract with MTN on 23/11/2019 but to my surprise i was deducted R5464.26 was deducted in my account and when i call them 1 consultant confirmed that yes they did receive my settlement amount and i have closed and she tried to transfer me to retention but no answer call ended and call again another consultant said my account was not closed and it was then upgraded which i was not aware of and they have been billing me please assist me as they say i owe them that five thousand and some change