It is a phishing scam. All they want is your personal information. Just like the Nigerian 419 email scams. Telemarketing scams are on the rise.
Never respond to unwanted robo or unknown robo telemarketing call and NEVER PROVIDE PERSONAL INFORMATION over the phone. The criminals will use another number shortly and try again.
Another helper is this... most cellphones have a "ringtone" which is actually NO ring at all. Plus, you can save numbers in groups & assign No Ring to the group, & it'll cover any #'s you add to that group at any time. I have about 75 scammers who keep calling my cell, but I never answer cuz the phone doesn't ring.
I also assign "friendly" ringtones, so when I hear the old ringing-phone sound, I know it's a stranger.
& As many have said, if you don't KNOW the number is legit, DON'T pick up, & DON'T call back. They really do use computers to constantly ring-&-hang-up, one # & then the next, to see if it's a "live" line. If you just ignore 'em, after a few calls (a few days) the puter will mark you as "number not in use."