Contract upgrade failure

I took a SIM only contract that lasted 24 months with MTN until it expired. When it did, they gave me a new contract without my consent. When I complained and asked that it be canceled, they sent me a form to fill and email back. I did that, but I never heard from them again. When I called, I was told to upgrade my old contract so that the new contract will end. I did not want that but eventually decided to upgrade. Still, they cannot upgrade my contract and they don’t tell me why. I have tried three times already.