Cell c billing me for a phone contract i do not have4

Good day

I had a phone contract with cell c from December 2019 and it terminated on December 2021. I paid all i owed them in December 2021 and went to upgrade, however i did not qualify. But not cell c is still charging me for a service im not using and they send threating emails to hand over my account to their attorneys. I do not have a contract with them and made it clear that i do not want their month to month nonsense contract but every month end they still force a debit order and also charge me for that failed debit order. This is theft. Cell c is acting *********ly. Its disgusting that they want to continue robbing.