CAN NOT GET CONTRACT CANCELLED

My son signed a contract for Wi-Fi at home @ R499pm, the Wi-Fi worked for 1 day, we reported it several times but nothing was done. Even though we had no service from this amounts in excess of R1,000 was deducted. I went to Montana Branch where the contract was signed to cancel the contract, and was assured that it would be cancelled and refund arranged. We heard nothing for 2 weeks, and went back to Montana branch only to be informed by another agent that they can not cancel the service. I have send mails to Telkom and to date still no service and no cancellation and still amount exceeding contract amount is being deducted?