Unauthorized Debit Order - Contract Cancelled

I have cancelled my contract with MTN in October already. On the 4th of November I have complained about MTN on this platform and no one has contacted me as yet. On the 1st of December they debited R350 and again today they debited the same amount and I don't have the WiFi with me. I have tried to call them and no one answers their phone. Please can someone assist me