It's the survey scam.  Call back gets, "Thanks for calling, the survey you were called for is now finished..."  Even if you call back within a second of their call, this is the message you get."  The scam goes like this, you get a free something for answering a few questions.  Some people report that the so-called free gift is a wal mart card for 100 dollars, some say they were offered free Disney tickets, etc.  After you answer the questions you'll be asked for a credit card number to process the small handling fee.  There ya go.  Not free if they need your  credit card.  Block it.