Get Caller ID and screen out calls from names, numbers, places you don't know.  Everyone who answers and/or calls them back just reinforces their behavior.  Call blocking may discourage them for that particular call but they use robo dialers which don't care and they keep calling as long as you encourage them to continue with their game.  Complaints to DO NOT CALL or states attorney generals, even the FCC will not help.  They have so many complaints from so many people about so many numbers, they could not do you any good even if they wanted to.  Worst you can do is respond and vent; then they know they've got a live one and they will continue........