Why would you call back a number that did not leave a message for you? People like you are perpetuating these scammers because now they have your number as "live"..................... and everyone else who calls them back or answers the call when they dont recognize the number.
Folks, do you have voice mail? Most likely. Then let these people leave a message if its so important. More than 9 of 10 times you'll come to find these are just scammers.