Continued debiting my account after cancelling

We opened an account for my son that was suppose to be a top up contract, only to find that it was not a top up contract. We then contacted Vodacom, and asked them to cancel the contract, and the collected the phone and the sim after a month of informing them. However they continued to debit my account. for several months. I then called them and asked them to please credit me the amount and to stop debiting me. They then ceased the debits for 6 months and then started debiting me again. Unfortunately I did not notice this until the end of the contract, when I was trying to close my banking account. I have since called them several times, and asked them to stop debiting me, and to please reimburse the moneys they have taken. It has been about 4 months now and I am still waiting for them to stop trying to debit the last amounts from me, and to reimburse my money.