MTN contracts are a ****

My mom cancelled a contract she had with them and even paid the cancellation fee of R2500 and this was in 2023/03/23 and we were told that they will deactivate the sim card and spot the debit order as we cancelled their service and paid the cancellation fee .. they had the audacity to take my mother to credit bureau. Saying she owes them ..I have the cancellation proof of the amount we paid and we cancelled it in Bloemfontein mimosa..