cancellation of contract

TWO weeks ago, I asked mtn to cancel my cellphone contract. It took them 5 days to sent me the cancellation fee. I then paid the amount for cancellation the same day. That was last week Monday. I even received a confirmation of payment. But still they have not cancelled my contract. I don't know what else to do to get this contract cancelled. They must transfer it to pay as you go.I tried several times to call their call centre but the number keeps disconnecting. Please could you assist? I already paid all the cancellation fees. The reason for cancellation is their bad service. They are forever disconnecting my phone for no reason when I need it most.