Them: "Our phones are down."

Me: "I'm sorry to hear that. Have you notified your provider?"

Them: "My provider?"

Me: "...You haven't been our VoIP client for about a year and a half now."

I got called at 2a once because someone thought our company was the makers of some shareware software and they wanted support. When the screens didn't match my memory; I walked them through setting up screen share. I saw that wasn't our product, I couldn't help them, and hung up.