Breach of contract

I took on a R200 top up contract with MTN. Head office has placed me on the wrong contract. I was slapped with a bill if R16000! The line is now suspended and I am still not put onto the right contract. 3 months have gone by without any solution or assistance. Each time a new person handles my query through customer care where I explain the situation repeatedly and none have helped so far. Nobody can contact my number which I kept for 5 years and if I cancel my contract I am told I will lose my number which initially was prepaid. I am so frustrated. The incompetence and lack of urgency is disgusting. MTN is just useless. Don't ever use them for anything. The last time I also took a contract with them a few years back. They had given my number to someone else whilst still charging me every month. It baffles me how they are capable of doing such things? It's like they're a giant network *****!