Call back gets "The number you have dialed is not in service." That means this number is SPOOFED and that spells SCAM. If they're hiding their identity behind a spoofed number, they're lying. That's the best reason in the world to never answer and block the number.
well I just got a call myself .. but i have figured how to keep them away .. I simply answer ... " thank you for call the federal dept of investigation how may I direct your call?" I usually get an " Oh s..T !" and they hang up never to be heard from again ...