Continued deductions on an expired contract

I informed MTN that I no longer want their service due to lack of coverage. Here are the facts, as in the letter I sent to their complaints. And there is no response, except for taking my money!

"I entered into a data agreement for 12 months as from 27 June 2021. The contract was changed to a pay-as-you-go agreement.

On moving to Mookgopong, I informed the call centre that the contract must be closed, because of poor reception. I gave the customary 30 days' notice. They persisted in trying to keep me as a customer, although I cannot use the data supposed to be provided.

I did everything required to ensure the contract is closed: I informed the call centre, requested closure, listened to arguments contra, insisted on closure, gave 30 days' notice, responded to SMS's asking for confirmation of decision to close.

Finally when you informed me on 27 June 2022 that you intend to deduct from my account, I informed you twice on separate days, that you are acting outside the agreement by continued deducting of funds from my account.

Today, 2 August 2022, you again deducted an amount of R177.55, which is actually more than what was originally agreed upon.

I now demand that you 1) Refund the monies deducted ultra vires 2) Stop deducting payments by debit order or any other means. 3) Stop harassing me with advertising or "friendly" notices"

It seems as if once a customer, always a customer - they will never let you go. Or am I wrong?