Incorrect Debit Order, again, After Contract Cancellation

I am formally lodging a complaint regarding the mishandling of my contract cancellation and continued billing. I cancelled my MTN Home Internet modem on 21 February and received confirmation of cancellation on 22 February. Despite this: A debit order was processed on 1 March, which already included an additional cancellation fee. On 1 April, an even larger amount was debited—significantly more than both my normal monthly fee and the March amount. I have made multiple attempts to resolve this matter and have requested: A full reversal of the incorrect April debit. Confirmation that all billing and debit orders have been stopped. To date, I have received no resolution. To make matters worse, today (3 April) I received yet another notification indicating a debit order scheduled for 1 May. This is completely unacceptable, as the contract was cancelled over a month ago. This situation reflects extremely poor service and lack of internal control.