Ridiculous Service!

I had a 1 year contract with cell C from January 2014 to January 2015 for 10GB of data per month. I came into the branch before my contract ended to cancel it as I am no longer working and am not able to take up another year contract. At the branch they told me it was no problem as my contract was coming to an end so they will cancel it. They told me it's my final month so I can just see it through no problem and then the contract will be cancelled. THEY DID NOT TELL ME TO PHONE WITHIN 24 HOURS!!! I assumed all was sorted, used up my final 3 or so GB of the 10 for the month (as i try to monitor my usage each month to ensure I stay within that). Then I get a bill of R1399 in January from Cell C. I was extremely confused and went into Cell C. I told them my whole story and they say that because I did not call my contract was not cancelled. I have a witness to the fact that I was not told about the compulsory call. I now only managed to cancel my contract in February which means I have to pay for January and February! I am LIVID !!! They say there is nothing they can do but I am NOT WORKING. how the HELL am i supposed to pay for THEIR mistake?!?! I will NEVER deal with Cell C again.