Harassed for paid up account

I'm am very unimpressed with these. They are harassing my elderly mother with a SARS bill that I have personally settled. We have sent proof on all of their communication platforms, which they respond to days after the time. My mom had to go to SARS to obtain a statement as we could not obtain proof via efiling. We posted on all digital channesl and called these people,to date every week, mom still getting emails harassing her about outstanding balances. They are not reconciling their records with SARS systems and really ought SARS should rethink their collections strategy or the debt collectors they are using.