Call blocking will not stop scammers.
To block a call you first need to know the number that you want to block. That means the call first of all has to get through to the recipient in this case your parents so that they can block that number.
It is a pointless endeavour trying to block scammers because they use spoofed phone numbers and they also use an infinite number of computer generated numbers which they use via an auto dialler so as to avoid call blockers which can not possibly block all the computer generated numbers which in many instances are only used few time by the scammers.
As has already been pointed out you need to get a phone that will only allow "white listed" calls through. You control what the numbers are that get "white listed" such as those in your known phone contacts Family, Doctors, Banks etc and all other calls get blocked until they announce who they are.
Scammers obviously do not want to announce who they are plus in most instances the scammers call is initiated by an automatic call dialler which only passes it onto the human scammer after it has been answered by a human and in this instance it would be an automated answer requesting that they state who they are by which point the scammer or the automated dialler will just hang up.
You or rather your parents need a phone that can white list callers, not a call blocking system
