who's using ?

I get phone calls a few times a week from this number.  I tried to look it up but it can't be found.  When I answer they hang up or I get a busy signal.  Who is it?  Is it a phone card or what?

Calls between 10 and 11 p.m. Every night! Comcast says not a real number so cannot block it. House phones are Panasonic and they will block it, says it is a foreign group number. Probably trying to spoof our number. They have home number and one of our two cell numbers.