Ill treatment

My father is using Telkom and pays R139 monthly. On 29 October he was called by Telekom agent that he is owing R335 and they are suspending his account and handing it over to the debt collectors. We went to the bank as the acc is paid via debit order and we forwarded copy of the statement to their whatsapp number only for the debt collectors to call on 2021-11-08 saying my father is owing R1500. There has never been any single non payment to this account. No one is assisting as we try all the channels to communicate with Telkom but failed