Paying for a cellphone which was returned

I upgraded two of my contracts in 2013, both were for the blackberry 9320 curve, upon receiving the phones my husband decided that he wanted a LG cellphone, I sent one of the blackberrys back with RAM couriers and went to cell c in the promenade, mitchells plain to get the LG phone. Nicole Koopman assisted me and was told that she could only let me have the LG once they received the blackberry, which she was able to do. However I have been paying an additional R79 for BIS for the blackberry which was returned, since September 2013 up until December 2015. I have seeked help from ICASA which was of no use and have been to many of the cell c stores and have been told that they cannot assist me as they are only a franchise. I have been with cell c for 8 years and I have never had issues with them up until 2013, I am very disappointed with the type of service I have received from them and will not recommend them to anyone.