These jokers can spoof your caller ID. They can make it display any number, functional or not. If they wanted to they could send 123-456-7890.
If you don't know the number. Let voicemail catch it. You can always call back if the call is/was legit..
Unknown Caller, didn't pick up when called. Searched online to find out who this was later... there is no records. Called the number back and was prompted by an automated voice saying Ive won some kind of gift card to be used at popular stores. It didn't say how I "won" this. Automated woman told me to hit 1 to accept this "gift", however I hung up instead.