I am frustrated with MTN

I am frustrated with MTN . Last year December, I terminated my contract and I paid the full amount. Then last month I received a statement stating that I owe MTN R250. I was confused because I had paid the settlement amount. I called the MTN call centre last week Wednesday & I was told that the person who was assisting me last year made a mistake & didnt do an immediate cancellation. They said they will escalate this since it wasn’t my fault. Till today I haven’t received any response from MTN. The MTN retentions department isn’t helpful either. Their team manager he said his name is Siyanda, promised to call me back with answers & till today he hasn’t done that. MTN , I need answers & I want this matter to be resolved Right now MTN is just giving me a run around & they are refusing to help me. What frustrates me more is that this is messing my credit score because of what their employee did