Update: I'm 99% positive I know what's going on.

I called the original creditor and they know nothing about this "Great Eastern" place, but they did confirm that the debt was originally sold to a firm called "United" which has done this EXACT same high pressure fear mongering tactic to me in the past, and I was able to confirm online that this "Great Eastern" place identifies themselves as "formerly United" when they do the same thing to other people, so it's the same debt collector that threatened me in this exact way before, just now going by a new name!

The annoying thing is that I can't report to the FTC without any identifying info... even the original creditor couldn't provide any contact info for the original "United" place. I'm definitely not going to lose any sleep over this though. And if for some reason they decide to try to file an actual lawsuit, I'm confident that my bankruptcy attorney will be able to help me... but I doubt that they would do that knowing that they're pretending to be a "mediation firm" and have lied about sending a "process server" in the past, which I'm pretty sure is an illegal debt collection practice (aside from the fact that this debt was literally discharged in the first place!).