Unauthorized debit order by Telkom Mobile

In November 2017 got into a data contract which expired in October 2019. I stopped using the service in September as the network connection was poor where I stay until the end of contract. Got a call from one of the agents enquiring if I was interested in an upgrade. I indicated that am cancelling an not upgrading. To my surprise, my account was debited in Nov & Dec and when I asked, was told that am now on a month to month. Was advised to call in again and cancel which I did but still in February once again my money was taken. I keep stopping the debit order but they now even send me a bill with fees for rejecting the debit order. Is that even lawful? The contract ended in November and I did call to let you know that I am not continuing with the contract since I was never using the data due to limited connection. The lady I spoke to in January confirmed that the contract was terminated and I don't owe anything. Please help!