Harassment and ******* Deductions

I have not a contract with MTN since somewhere in 2020, when my contract ended. I did not renew it and after a few months I noticed that they are still billing me for something of which the contract period has expired. I contacted them at the time to query, seeing as I also sent them an email informing them that I am not renewing my contract. But now every few years or so they pop up as they now done again for the first time in about two years to attempt to deduct between R 2500.00 and R 3500.00 from my account. How do I stop MTN from trying to rob me like this, I don't own any MTN product and haven't in more than 5 years. I do not know what to do? Life is expensive and we can't have Providers robbing us.