Who called from 9412001999

no caller id; first time I ever saw that! Left no message.

caller id Voip number. no message.

Hang up no answer

They called, I answered. They said nothing and hung up. I called back and got recording number was not in service.

Same thing happened to me - they said nothing and hung up.  I called back to get a "this number is not in service."  Some type of scam or telemarketing.  I reported them to the National Do Not Call Registry.