Contract ended and was cancelled. Unauthorized debt orders continue

MTN does not know what it means for a contract to end. Sadly neither do they understand what it means as per their policy what it means when I customer states in writing and via telephone that they will not continue with a contract which has come to end. I am saying this because they keep debiting my account although my contract came to an end mid March. A month before I emailed them and called to tell them I won’t continue with the contract. I was then advised to call again a day after the actual day and I did. Both my numbers where they turned into pre paid. Furthermore, I forfeited all my contract data, airtime and minutes. So then why the continued debting? My account is now in a minus and I expect MTN to pay it.