cancellation of contract

I am very disappointed with the Cell C provider. I am having a sim card contract for the data, whereby I was told in case If I want to cancel the contract I should put a one month notice in order to be cancelled. The reason why I want to cancel it is because I installed a WiFi at home therefore it is no necessary to have it anymore. I called Cell C it is for the period of 3 months now,but they are not intending to cancel it. They are making me a fool by transferring to various dept. and again dropping the phone so I am tired of their games .