Every now and then I hear advice to the effect that saying even a single word to a robocaller will get your number flagged for more, so you should just answer silently and hang-up. Whenever I follow that advice, I get more and more calls. Then I start engaging with callers to waste their time and resources. I press numbers, try to get to speak to a human, and then generally mess with them if I do get a human. That usually takes care of the calls for a while.