Account closure

I recently called MTN for a settlement amount so I can pay up the acoount. They Gave me a settlement amount of R3319.53, which I paid in full. They then sent me a email confirming that there is a outstanding amount of R953. No one can explain where this additional amount is coming from. I went to the Cradlestone branch to find out what is going on with the account. The consultant wasn't really helpful, he didn't even give me an alternative to sort it out besides from telling me to call the call centre. I can't get through to a consultant on the 083 135 number. I want to close this MTN contract ASAP because their service are ridiculous, very unhelpful and have no empty for their clients.