service failure

I had a contract with Vodacom from 2018 and It ended 2020 November but I paid it before then. I did the payment and the person who was helping said my contract is closed and they have moved me to prepaid. I'm busy receiving emails to say that I am owing my account is overdue I don't know what account they referring to because my contract is closed. I was applying for a loan it declined and said my Vodacom account is in arrears and what I know is the account is closed. It was a mission for me to get the account closed. If I knew that to get the account closed it was gonna be a mission I woudnt even have bothered to be part of them.