Stick with it--Don't let them wear you down, and I can tell that you're not.

Also, fuck that rude prick. With the evidence you have so far, you are on solid ground and asking the right questions. That they cannot provide answers is on them.

And in the rare couple of times in my life when I was getting nowhere with a utility on an issue, I found that mentioning to them that you're reaching out to the Dept. of Public Utilities (Mass DPU) has suddenly made progress appear where there was none previous. YMMV but it's an option--either to actually do it, or play the card with NG before resorting to it.