COntract cancellation done but debit orders continue

I am very unhappy. On 19 October I phoned in to cancel my MTN contract on the above mentioned data no. I was assisted by Nondumiso who said she would change the number to prepaid and it would only be effective on 17 Nov. And that end of October 2022 I would still be held liable for full amount of the out of contract data bundle. I understood that would be the end of MTN withdrawals from my account. I was given ref: *** as my cancellation reference

To my surprise MTN on 01 Dec MTN debited my account again and I have incurred costs for unpaid amounts due to this.

Please can I get assistance for refund for the full amount please