Call blocker might be of some help. Also don't pick up on numbers you do not recognize, or where there are caller IDs that seem odd. Or where there is no caller ID.
Got a call yesterday from VA B as it showed up on my phone.....732-290-9782 and they asked if I would be willing to put in an alarm system for free and post a sign on my lawn then the man asked if I had a home monitoring system already installed in my home, when I gave him my answer he quickly hung up.....I have been suspicious and the call stuck in my gut. tried to call back today....call is scrambled and then busy........I AM ON TO YOU.