Who called from 5715580000

Got a call from someone purporting to work for a government agency they couldn't name due to security concerns.  They claimed they saw an ad for an apartment rental that listed my phone number.  I have ran ads for a room rental, but not with the number listed.  Very strange call.  At first the person claimed to be a young woman wanting to get her first apartment.  When I asked for her name and number to call her back, she said that she was married with grown children and my rental wouldn't work out.  Very strange.

Got a 6 am call from this number but I didn't answer because it was 6 am! No voicemail left.

Got a call from a woman claiming to set up an interview.  She spoke real fast and I couldn't understand her.  I thought it was a sales call at first.

This is NGA - National Geospatial Intelligence Agency.  All numbers originating from their building will show up with this number.

Got a call from this number and the gentleman left a message with the name Simon and wanted me to call him back at 301-502-8327.  I did not call back because Ido not know anyone named Simon, and if he wanted me to call him back why didn't he call fromt hat number it he first place.