MTN is the worst

MTN is the worst mobile service ever. Their policy says to cancel your contract 20 to 30 days in advance. I submitted cancelation on the 17th of Oct 2023 and on the 20th of Oct 2023 I was sent confirmation that the contract will be cancelled on the 26th of Nov 2023. Then by the end of Nov I start receiving notices of a contract upgrade and invoicing. I called the helpdesk to try to explain that I'm no longer using their services. Either the call gets dropped or without notice I'm transferred. Now their customer services recognize the cancelation but their billing department still keeps sending invoices and debits my bank account. And no one seems to be able to stop this. No one takes responcibility.