Continued overcharging

Early in 2014, Cell C started calling me to get an upgrade. Unhappy with their service particularly the billing, I opted not to upgrade and let my contract ran out. For the next 5 months of the remain term on the contract, my bill suddenly became R300 -R400 more despite no change in actual usage. <br> <br> I then renewed the contract in the hope that this trend would stop (and because Cell C still has the most cost effective deals around) but unfortunately it did not. Cell C went as far as to charge me the extra charges for two months when my phone had been reported ****** and was not in use. <br> <br> I have contacted Cell twice and have had no response.