Cell c and the never ending disappointment

Again cell c has been completely pathetic!! Once again they over charge me, ***** with my money. So I go into the store to find out how I go about giving my phone back and having my contact canceled, with no cost to me of course, since I have had such a horrible experience with cell c. I think it's only fair that they accept how horrible, terrible, pathetic and useless they are as a company and at customer service, and they just cancel my contract so me as the customer can just move on from their ****.. And they can move on too... But of course not! They won't take my phone back and cancel my contract.. So I need to know how I go about taking legal action against cell c.. Does anyone have a legal suggestion?