Who called from 2123044587

Called my cell also-don't know who it is.

I have been getting calls from this number over and over. When returning the call, there is a message saying this number is not in service.

The phone rings and this number appears; no one is at the other end. When I call, it is a number not in serve

all the time

Called me 3 times in 3 days.  No answer everytime and when I call the number back a fake-sounding "this number is not in service" message plays.