Note, please, this is only one of many scams spammers are running as they shift their attention from email spam based scams to dialing-for-dollars scams run over phone systems. Don't be fooled just because the scammers use the telephone to run their felonious schemes rather that using email.
Why the shift in their attention? Simple, spam email no longer is profitable because finally consumers are paying some attention to spam, and deleting email from sources they do not know unread, and response rates verge close to zero for many of their campaigns.
The same principles apply to spamming telephone calls. Aggressively screen caller IDs. If you do not know the caller, do not answer no matter how legitimate the caller I'D may be. If you are fooled and do answer the call, immediately hang up. Do not worry about the sensibilities of the caller, I promise you that they do not care about yours. Do not engage the caller in any discussion, that only gives them some idea how to pin-point future spam calls to try and make them more tempting. Hang up is the new delete in the phone scam world.