I had a similar problem with phone scams for my elder parents. Installed Asterisk with a Raspberry on their land line to allow only whitelisted numbers and the problem was solved. I guess someone has to step in at some point. Problem is not every parent has a tech literate child and the industry doesn’t seem to bother to offer decent solutions. All call blocker hardware that I found didn’t allow whitelist functionality. I guess there’s a business opportunity here easily, build hardware/software solutions to protect the elderly.