My home phone rang.
The caller said
"Good afternoon, this is John from the Technical department of BT Openreach, calling about your broadband connection."
Me: "OK John, would you be kind enough to give me your nine-digit EIN please, so I can verify you're who you say you are?"
As it happens I am at home on leave today, but it would not have taken very long to fire up my Openreach computer and verify the number if it had been a genuine call.
Since "John" instantly hung up I think we can be pretty certain he wasn't who he said he was.