Dispute towards MTN

Good day MTN handed my account over to Nudebt, after doing so I paid of the account within 2 months and the account was settled off in February 2024. They then sent me a paid up letter and Nudebt closed the account from their side because it was paid. Up to date MTN still says that I owe them R7215.16 after several emails that I wrote where I cc'd Nudebt in the emails still MTN doesn't want to clear of my debt they still say I owe them.