constantly calls but does not leave message!

Calls every day, all hours.
I'm signed up for not getting unwanted calls.

Call several times a day. Don't leave a message. Says from Pittsburgh, PA.

I've received 5 calls since early March 2010 from Outreach Associates and the caller today said they are fundraising on behalf of Unicef.  When I asked who was calling they said they were fundraising on behalf of Unicef.  I hung up and then called Unicef, told them about my call, and the woman I spoke with was not aware of Outreach Asociates.  She said she would send an email to someone in the Unicef organization to respond to me as to Outreach Associates legitimate status on fundraising on behalf of Unicef.  Then I called the number 412-773-8568 and there is a recorded message saying that you should leave your name and phone number for a call back.  How do these organizations get your name and phone number when you're on the Do Not Call list??

I answered but no one was there. I'm on the no call list, but that doesn't seem to stop many people these days.