My question is finally answered today by an All Tech Considered report on NPR.

• The bad guys are using robocalls to check if your phone number is active.
• Once that’s confirmed their computer calls you again, trying to get your personal info to get into your pockets.

The banks are using Pindrop Security to filter out fraudsters but there isn’t much there for us consumers.

What can we do?

• Just Hang Up
• Do not talk, do not press any number!
  I once did that by mistake and the call kept coming for many hours.
• And only call numbers on your debit/credit cards and statements.

Also read my post on unsolicited robocalls.

Please be sure to play the clip especially for the older, less “connected” people.