MTN billing months post cancellation of contract

MTN is still billing for a contact that expired in October - and which I went into a store to cancel on the 5th of that month. I was told that, although I had paid for October, no more data would be available. I should, I was told, have read the fine print to know this. That not being bad enough, MTN has now deducted the contract fee for 2 more months. The number given for Customer Care on the invoice has a message 'this number does not exist' when called, and no other number I have tried gets to the call centre. I have stopped the debit order, and am required to let mTN know this- but am completely unable to do so. Definitely my worst experience ever with a service provider.