It's the telemarketing survey scam.
Call back gets, "Thanks for calling. The survey you were called for is now finished." This robo "survey" is how the telemaggots get around the DNC regulations. There is no survey just some nonsense questions. You'll be offered a free something for completing the survey then asked for you credit card number. It's a SCAM. Block it.
http://www.ag.state.mn.us/consumer/Publications/SurveyScams.asp