no message, just hangs up after you answer

i am getting lots of calls from this number and a few others that all announce (by a recorded message) "if you are a senior citizen, you might.... then sales pitch stuff.  I can't block the calls. then the calls start coming from other numbers,but with the exact same recorded message.  
If anyone knows how to stop these calls, I'd love to know what you did.

An unidentified company, they left a LONG prerecorded message on my voice mail (it filled up my voicemail, blocking a call I was waiting for), pushing medic alerts for seniors (of which there are none at this number).  They've called before from different numbers.  If you call back, you will get the same recording as the one they leave.  Of course they are always too busy to answer, and will just have you leave a name and number.