got a call, and they hung up

I am tired of getting calls from this number!!  All they do is continue to call and hang up!

The same, don't know who they are, called and hung up once my answering machine picked up.

rec'd a call from this number. same thing nobody there.

Yes, I answered, silence, line goes dead.  Are these people canvassing who's home and not home, and then selling the info' to criminals?  This is not the first time I've gotten these annoying ones.
I got another earlier with CID of  "NAME NOT FOUND 123-456-7890"    
It's easy to spoof caller ID's for there seem to be no regulations about that.Come to think of it, what about the "Do Not Call" list?   Useless, I've been on it for years, and get unsolicited garbage calls.