Feeling very cheated by Cell C

Last month I call your call centre to cancel my data contract which was ending on the 20/02/2015. Since I was concerned abt being charged for a full month I was reassured by your call centre agent that I wasn't going to lose the data that I still had and that my sim card was going to be changed to prepaid. Then I check my statement and to my surprise I got charged more than double of what I used to pay every month! I then get told that it's because I'm cancelling my contract tht's why I got billed so much! Like really Cell C. Then I asked in store as well what's going to happen with the data I still had since my contract end on the 20th, even there I was reassured that I would still be able to use my remaining data and that the sim would be changed to prepaid. Come the 20th the sim card is no longer working AT ALL AND YOU TOOK ALL MY REMAINING DATA! For me Cell C that is CHEATING CUSTOMERS out of their money! On top of overcharging me you also ***** my data! After 6 years of being with this ****py network I just keep on get *****ed. So please refund me for my data that you took or give my data back coz I can't get half of what I've paid for on top of being overcharged this month!