Spam Calls

We are plagued daily with two or three obvious spam calls, ofren at awkward times.  We have learned that if there is a two to three second pause after we day hello, it is a spam caller registering at the other end of the line and we hang up.  A neighbour has let us know that there is a system to kill all spam calls but we don't know what it is or how well it works (although she says she gets no more spam calls).  Is there anyone out there familiar with a system to help us shut down the spam calls?

IanC