Over charge

I had a contract 4 2 years and was told that I will pay R99 for 5 gigs and 100 free minutes a month.I was told that I will pay R99 until I cancel my contract. I was up for renewal and was sent from pillar to post as the call centre told me they don't have a cancellation department and that I have to cancel at the store,2 stores told me I have to cancel with the call centre.I got a form from the store and was told to complete it and fax to headoffice which I did, was than told it will take 30 days to cancel and that I have to pay R349.My account was debited on the 27th December. I have spoken to numerous people and was told that I will only pay R99 and not R349 yet they deducted R349. I WANT MY MONEY BACK ASAP!!!!!!