Cell C overcharging

Cell C trying to take more money than agreed upon. My original contract is R299pm and now all of a sudden they are trying to collect R438pm. I have sent emails requesting to be phoned about the matter to no avail. This is me publically informing cell c that I WILL NOT pay you a cent untill you correct the amount. This is a breach of contract and according to South African consumer protection law it is with in my right to refuse payments that was not agreed upon. Also according to law if you breach the contract it is within my right to deem the contract null an void! I am more than willing to take legal action as I never agreed to any sudden price increases. The amount agreed on with your online department (Cell C direct) was R299pm. Correct it and you will recieve your payments, if you dont come and collect your phone!