Vodacom messing with my credit profile

I had a cellphone contract with Vodacom, I paid it off and closed the account in 2019, however my credit profile shows i owe then R835 and that my account is still active. i have called them countless times to get them to update my profile and send me a paid up letter. They have promised to send it but till today they have not. I over paid my account with R29 they owe me that R29 yet they claim I OWE them this is badly affecting my credit profile