I've done that a few times until I got bored, then when they think they've "got" me, I let them in on the little ruse...they're surprisingly fluent in English swear words...some rather nasty!  ;-)

Ever wonder how these crooks get your numbers?  It's really simple!
These pukes have robocallers that work similar to this:  your phone rings, you answer it...and dead air; the fact that you answered it or your answering machine did, tells them that it is a working number.  Thousands of these things happen every day and phone lists are sold all over the world.  Then the scammers, who are able to spoof numbers to make it appear that they're calling from one part of the country....or the world, for that matter....when in fact, many of them are calling from a boiler room type of environment in India - and other countries (usually given away by their strong accents).
The first thing all of us need to remember is that NO ONE is monitoring our computers (such as Microsoft), and our computers are NOT sending messages to anyone.  As for them knowing our names and/or addresses (in some cases), if we're on the internet a few times a week, that information is seen by many, many people, but only of interest to those wishing to scam us!

The do not call list was a great idea when it was conceived by someone, but for the most
part it's a waste of time and does NOT work very effectively!!!

this guy ..said he had grant money for me 7 thousand .  I replied that I am sorry I don't deal with scams and he hung up on me in the middle of my sentence

Just got a call from whoever it is.  I didn't answer.  First thing I do with unknown numbers is turn the phone off, then I look up the number online.  If it's a scam, a scuzbag and other assorted idiots, I go into my "Recents" list, find the number, and block it.  5 minutes of my life I won't get back.  NSA should go after these lowlifes instead of everyone.