Faulty Devices, Money Disappearing, Bad service!!

I have unfortunately been on a contract with Cell C for three and a half months now and have had nothing but issues. I took the Sony Experia M5 Duel sim phone, which has proved to be very very unreliable. I have over three months returned the phone and had it replaced three times. I have had major billing issues as money is disappearing from my balance daily and no one will sort the issue out. I could not send a single SMS for three months until it was finally fixed by a very helpful Mandisa (The only one to actually sort out an issue). I cancelled the contract on Wednesday and confirmed it yesterday to have Ram deliver 2 broken devices back to me this morning! I called in to Support to be told that the contract has not been cancelled and another phone is on route!! I do not want to deal with this company any more as they do not reply in truth and are dragging their feet on looking into and sorting the money issue. I have resorted to contacting their head office, but do not expect much from them whatsoever. Pathetic service to say the least. Take your contract and keep it! Doubt Cell C will give a care in the world on this complaint... they have not so far...