I suggest you get a BT call blocker phone or phones.
Since I got mine I haven’t had any nuisance calls.
You can setup a list of blocked caller numbers, any on this list get a message saying they are blocked and your phone doesn’t ring.
Any number in your directory gets straight through.
Any other numbers get a message asking them to say their name and press a button. Your phone then rings with their name played to you. You can accept the call, send it to answerphone or block it.
In use, any nuisance calls don’t even cause your phone to ring.
Stuart