MTN REFSUING TO CANCEL AN EXPIRING CONTRACT

MTN REFUSING TO CANCEL A CONTRACT. My contract was taken in August 2021,for an IPhone 12. Accordingly,the three year contract is due to lapse in August 2024. I called MTN ,now, a.month before expiry date to give notice. Then Bham!! Contract can't be canceled because I'm in arrears with R9000.?? Precisely ,how the R9000 debt accumulated, cannot be explained, because my debit order has been going through for the past 36 months succesfully