Billed even though I didn't use the SIM all month

I had a contract with Cell C which was purely a data contract for use with my iPad. My bill went from around R250 to R800 suddenly, and when I went into the store they informed me that my contract had expired (yet no one tried to contact me about it) and therefore they were charging me per megabyte. I spoke to a consultant in their cancellations department who was very rude but assured me he would follow up in what had happened. A few days later I received a phone call from another consultant offering me upgrade deals and explained the situation to her, of which she had no former knowledge. She then offered me a contract for R99 which I agreed to and she told me I would be charged on the first of October. When the debit order came off my account, the amount was R178 - which was not the R99 promised, and this all after not even using the SIM card for the entire month of October in fear of this very thing happening. I would like to cancel this contract as I have no desire to continue in anything with cell c.