Who called from 5131981078

This number, obviously a spoofed number (because the number is not in service when you try to return the call), has called me four times on 9/4/2013. I have answered within 2 rings every time, and there's no one there. Very annoying.

Stop calling

Two calls 2 hours apart.  Phone rings twice and when answered no one says anything.  Cannot find number on a reverse search