Telkom - still receiving an account for a bill settled 20 months ago!

My parents (du Randt) sold their townhouse at the end of 2019 and moved out of the property on 3 Jan 2020. Their phone bill on *** was settled but now 20 months later they still get demands for a phone line that does not even belong to them anymore. How many times more are you going to do this? This is typical Telkom (look at all the complaints!). Now this account has been handed over to P&P Attorneys ref 37D020663. Come on - for what? They are pensioners that do not deserve to be harassed for something that been resolved on more than one occasion. Please can we resolve this in writing (PLEASE DONT CALL) via email only. And can I receive an explanation.