Who called from 2173830573

I got a call from this number yesterday and again this morning.  Pretty sure it is a robo call and I do not know anyone in Chicago.  Can't understand why I am the only one to complain about this number.  ????

They called me on Saturday, Oct. 20th, 2015, Noon, PST.
They did not leave a message.

I received  a call from this number yesterday at 4:32 pacific time. Ignored - they did not leave message. They called again today at 2:13. Again ignored, again - no message. The call comes from Urbana IL ... Now it will be blocked.

No VM. I called back and number is "not in service".