Combat that by letting your phone ring if you can, or with a call blocker. Kind of hard to leave a message if there's no kind of answer from the numbers they call.
Just received a call from the number 751-783-1773 indicating I'm being sued by the IRS if I do not respond. I called the number back and let it ring until it disconnected it self (no one picked up).
Same thing as the others. Man with a very thick Indian accent claimed it was the IRS who is suing me. When I correctly pointed out that the IRS is located in Washington, DC, and not Riverside, California, he hung up. I called back and said, "you know this is a scam right?" He said yes.