Threatening debt collection yet cancelled multiple times

My wife had a Month to month mobile contract on her/wife name but was for my 18 yr old daughter for a few years. My daughter passed on 11 June 2024 and my wife cancelled contract in July 2024. Telkom stopped debit order for some reason and advised R517.44 was outstanding in Oct 24 . My wife then paid it and again requested cancellation in Oct 24 however started received threatening emails & sms's again now in Feb 25. What do we do? It is traumatic as it is and today being my late daughter's birthday have to put up with this!!? Mobile no: ***. Go and check when this account was last used???!!!!