Here is a practical suggestion you might like, involving faxex; in fact, I have it set up on my home phone. This works if you have "memo or message record" on your phone.
1. Go to the CIA web site (google search will provide it).
2. Write down the FAX number on that site.
3. Phone that fax number and record the beep on your "memo/message record".
4. Set up your greetings for an alternate greeting than the one you want normal people to get (on my Uniden phone I can switch greetings with one button).
5. Make that alternate greeting the fax beeps on your "memo/message record".
6. When the phone rings and you do not recognize the phone number or you know its one of them bad guys, just switch to the alternate greeting. They will then be answered by a fax beep from the CIA. If they have the nerve to send a fax, it will be received by the CIA, not you.
This sounds more complicated than it really was to set up on my home phone.
They call me all hours of the day and from multiple phone numbers. They try to sell you some car warranty scam. YES ITS A SCAM. Here is a list of phone numbers they seem to call from. If they call be rude and tell them to stop.