Any 911 operator calling because of hangups for calls to 911, will leave a message but it also shows in the caller ID who it is! And they call immediately after the hangup, not some other time.

I received a call at 5:36pm today from this number with the caller ID of "Not Available".
These are just scammers, no different than the other 500 calls per year I get from scammers.
Just another number I've now blocked on my phone.