Thieving cellc refuse to cancel or refund

I have cancelled my contract in june 2017 with cellc. Paid a cancellation fee of nearly R5000. Only to find out in January that they desided not to cancel as per my instruction but to use the money as installments. I have phone them numerous times with promises from the retention department to sort it out. Cancel my accound and refund my money that they deducted. Cellc are *******. They owe me overR3700 and dont care less about there customers needs. Im fed up.