MTN service with Home FLTE 1TB cancellation

My son had a contract with MTN, and he cancelled it in October 2024 after the 2-year period. He indicated he is not interested in any other service or contract. He received a cancellation number from them. The next month in November they send an invoice to him and indicated he is on a month-to-month plan that he did not agree on. He went to the Hartbee****rt Village Mall MTN shop and they told him there is no activity on his name and they cannot do anything about it. But it indicated on the mail that you can go to your local MTN shop and cancel it. This month again he received a mail that they are deducting an amount of R 1584 from his bank. If he does not pay, he will be blacklisted. How is it possible that they can put you on a month to month if you did not agree on this and now want to blacklist you if you do not pay. The Home FLTE 1TB is not even active. To correspond on the phone is to no avail some of them are extremely rude and our MTN shop is also pathetic.