Well he's not wrong. The moment you answer these calls your number gets added to a live phone list. I've literally had to stop answering calls unless its from a number I know. I did this for about a year and the calls trailed off to nearly nothing. Then, stupidly, I answered the phone before seeing who it was and all of a sudden I was inundated with these terrible spam calls again. Took another year before they puttered out again.
Don't answer the phone if you don't know the number. If it's important they'll leave you a voicemail.