Overcharged by Cell C

As my contract with Cell C was coming to an end I received many calls from their call centre for me to renew my contract. I was not going to renew as I was not happy with the service for many reasons. However, one woman phoned me, spoke incredibly fast and promised to give me the latest phone, double the amount of data and also double the airtime for the same price. I was paying R248.98 per month. When I checked my bank statement I noticed that they were deducting R346.31 per month. This was not agreed upon and she also told me that the conversation was being recorded. As I am a pensioner I find the extra cost is too much for what I use the phone for. I sincerely hope you can solve this problem for me as Cell C is very difficult to contact by phone.