MTN shift of incorrect arrears shifted to NuDebt

As a concern consumer I am raising this compliant about MTN. My daughter paid her account and after numerous efforts to get the credit amount moved from some 'holding" account, and this is after evidence has been provided, they handed her account over to a 3rd party. It is disgusting to see the efforts from MTN to provide client service and then after how many conversations with the 3rd party she paid the Invoice and then to get a second invoice after she made the payment that there is now an outstanding amount. Interest on interest is billed on a daily basis against the account which means as a client you will never be able to settle an account with NuDebt. The 3rd party agents behavior is atrocious to put it mildly, to slam the phone down is absolutely unprofessional. MTN is a well-known organization not sure how they feel about the association in terms of their reputation with this company. If the issue can be resolved without taking it to the Ombudsman we would really appreciate ref NuDebt ND***