d3's profile and activity

This number has called 5 times today, last was at 4:48 P. M. on 1/30/2013
Stop these people, limit to not answering, this # I answer, Hello, and no one answers.

5 different times this person has called. I respond Hello, no one replies so I hang up and do not answer the rest of the day. Name unknown 4:48 P.M. How do I stop this?