Many individuals, as well as businesses, help block unwanted calls by subscribing to a phone service called "Anonymous Call Rejection" or "Anonymous Call Blocking."
If you use a phone company's Anonymous Call Rejection service, anyone who tries to block their number when calling you will not get through. Instead of your phone ringing, the call is intercepted, and the caller will hear an announcement that you do not receive blocked calls.
If you do not wish to have the phone company screen anonymous calls placed to your phone number, or if they do not provide the service in your care, you can purchase a call blocking device in many retail and electronic stores.
The device intercepts anonymous calls so you do not hear the phone ring. Blocked callers hear a recorded message that you refuse blocked calls and they must call again without a block to reach you.