Telkom debiting my account outside the contract

I have had my contract with Telkom mobile from 2015 August and in 2017 August my contract with them expired. I called to cancel it and I was told to complete a cancellation form and email back of which I did. But they kept debiting my account and the amounts that they have been debiting are not even the same as the amount I have agreed. I have called many times to cancel by everytime they promise me that it will be cancelled in 24 hours but its never cancelled. And now recently I tried to open an account and I was declined because Telkom has painted my name bad. What I don't understand is that how can they even debit my account outside the contract? Is that not *****? And the amounts they have been debiting are all different. Please somebody help me to get my name cleared. I have kept all the emails between me and Telkom agents promising cancellation and acknowledging receipt of my cancellation form. Please help...