Who called from 2124329999

Called the office and I picked up and said "hello" it literally stayed blank on the other end. I called the number back and got the recorded message that it was not in service

Called my cell phone and I did not answer.  When I dialed the number back, a recording said that the number was not in service.

Called the office and when I picked up it and said "hello" no one answered. It literally stayed blank on the other end. Then I called and it back and got it the recorded message that it was out of order

This number has called my business several times.  It comes up on CID as "unbilled toll."  Did not answer first few times, just tried to answer, got dial tone.