answered but didn't say anything...call dropped in 12 seconds

This number showed up as "Health Plan 3" in caller ID. Third time today they have called, and each time I can hear someone on the line after I say hello, then they hang up. Calling the number back gets a recorded message saying "If you would liek to be placed on our DO Not Call list, press 1". Since this office phone is already on the Do Not Call list, they are obviously breaking the law.

"This is a public health care message..."  Female voice, something about qualifying for health insurance?  It's hard to remember what they say because I automatically stop listening if it's a recording calling me.  Called my private cell phone.