MTN post contract customer service sucks

So MTN suspended my account after finished paying off a contract with them that had lapsed. When I called in they tell me that I'm still owing but strange enough they had sent me a letter with my final payment. Now I'm not getting important calls and they don't care... But I'm supposedly a valid customer. MTN client service sucks once contract with them expires. I called in and we told the was now supervisor to talked to and that one would get back to me. Till now I'm still suspended with no call from them.