Kaiser

800-201-2023 has nothing to do with Angie's list.
For 800-201-2023 the resporg (owner) is Lightel telecom corp.  DBA LCI international 800-296-0220 8180 Greensboro Drive, McLEAN, VIRGINIA 22102, http://www.lci.com
The number is carried by Qwest 800-860-1020.  Only LCI can say how the number is used.
Just because that number shows up on your CallerId, it doesn't mean that's who called you. Maybe it wasn't even LCI.  Telemarketers spoof CallerId numbers every day.  Even though it's illegal.

Just now, at work, a call came in from (800) 201-2023.  No one
replied when I said hello.  I put the phone down on my desk and
in about 1 minute the call disappeared from my Caller-ID window.

The Angie's List possiblity seems right to me--I am an Angie's List
subscriber.  I think I will email them to ask them to not bother
me with this type of empty auto-call.

forgot to say - can't be Kaiser, they don't even operate where I live (in Ohio).

this number called, left no message and has no name displayed.

It's Angie's List, they called me from this number to ask me about some service providers I had looked up there.

They have been calling every other day for the past 2 weeks. I tried calling the number back. Nobody picks up. This continues to be frustrating.

They had no caller ID until a few days ago. Now it says "Kaiser".

This is Kaiser's collections department. This number is listed as a contact on your co-pay bill, just try calling it: there's no ringer and it ends up with a busy tone and hangs up on you.

I have seen this number before several times but they have never left a message.

They call, let it ring once, and hang-up without giving me a chance to answer, or even for my voicemail to pick-up!  If they are trying to get something from me, they are doing a poor job of it!!!