CAN’T CANCEL A WI-FI THAT IS NOT CONTRACT WITH MTN

I took a Wifi with MTN last year August, little did I know it would be the worst decision ever. It’s the R269 one, it’s not a contract, it’s paid on a month to month basis according to them. I used it in August, mid August i started having network issues, didn’t pay for it in September then tried to return it end of September they didn’t take it because I should’ve paid the September bill even though there wasn’t any data provision that month. Finally, they took it around November when I told them I can’t leave with the Wi-Fi! However, till today they still try to deduct the money and when I call I’m told to pay an amount of R2700??