called and left no message multiple times on multiple days.

They are harrassing and calling nonstop 3-7 times within 15 minutes. It is ridicuolous!

Based on reports elsewhere, it appears to be a collection agency which is violating the law.

If I thought they were a legitimate operation I would suggest you answer the call, get the address from them, and start with a validation demand.  But given the way they are operating, a call blocker might be a better choice.  

Google Voice is free and doesn't tie up your computer.  Panasonic makes call blocking telephones.  VOIP providers such as Callcentric offer good filtering.  Search the Internet for other options.

Collections agency for UIC medical center.  Cannot confirm what supposed charges are for other than date that I went to doctor.  Caller blocked.

This number calls me 3-4 times a day, on my unlisted cell phone whose # I have given to three people, period.  I Have never been to the U of C for any medical procedure.  They have been calling for about a year and a half. When you answer it's a recorded message that says 'this is not a sales call, please stay on the line for an important message"  Finally, today I did, I'm so fed up, but after literally 23 seconds and no one ever coming on the line, I just hung up.

I have a WIN 7 phone, which in IMHO sucks rocks,  and there is no way to block calls.  I actually went out and bought a new land line phone that has this feature because  I'm being harassed to death by another # I've listed here a few times.  I'm about to go pay the penalty for getting rid of my phone before my contract is expired so I can get a phone that blocks calls.