Ideas?

No message. I despise it when they do that

This number has called me three times and they do not respond when I pick up.

Called three times today.  Two of them I wasn't in and they didn't leave a message.  Third time I answered and no one would respond.  I posted an ad on Craigslist today so I thought it was someone responding to that.

Called me three times today, left no messages. I finally answered on the third call and they hung up on me. I called back and the operator said "that is not a recognized phone number."  Somebody needs to get to the bottom of this...