Who called from 2175576648

Had two calls from this number on my caller ID 30 minutes apart today while I was out.  Since I know that the IRS and other taxing agencies always contact people by letter I agree that it must be a scam.  I have no intention of calling them back or answering further calls from them.

I get random calls from 217-557-6648 sometimes a few in a row. I try calling back and it's always busy. When I answered once they just hung up.