Extremely poor service

I bought a new phone from Cell C the Glen. 10 day later the phone stopped working. We returned the phone on the 22nd November 2015 and by the 11 December 2015 nobody has contacted me to update as to what has been done. We have been to the store 3 times and all we here is that the phone is with a technician. This is extremely frustrating as Cell C has had the phone for longer than i have. Just by the way the debit has already come of my account so Cell C is being paid for a phone i dont have. Do i need to put up a billboard to get any help!!!!!8