Called, left no message

I get calls from this number and there is nothing on the line when I answer.  I called it back and a woman from a security system sales "robotically--but said a real person" tried to promote sell their security system.  I asked them to take my number off of their list.

Received a call from this number, caller ID says Charlotte, NC.  Answered it, but they hung up.  Guess they just wanted to see if it's a working number so they can pass it onto other telemarketers.  It's on call block now.