Texas

I did get hold of Centerpoint, who gave me a number that turned out to be for TXU. So I called them. Turns out you don't have to prove you live at a place to get a retail electric contract there. My power had been switched all right, but under somebody else's name. I remarked several times that it was ridiculous that I had to prove I was me to even talk to them about it, but the person who caused this, whether accidentally or maliciously, didn't even have to prove they lived here.

The part about not having to verify that you lived there, or at least had some connection that made it reasonable you would want a power contract there, was confirmed by both Constellation and by TXU.