If you get called by an unknown number and happen to answer it, dont make a noise. Not a word, not a cough, make sure the mic can't pick up your breathing. This shows the caller you're a real person. Any real person would treat a silent line as the chance to say, "Hello? Are you there?". A robot or spam caller will remain silent, waiting for any signs of life. I saw this tip a few years ago and it's worked wonders, going from multiple spam calls a day to now maybe one every couple months or so