This doesn't sound good. You don't say where you are located, but, if in the USofA, there are several English trained barrel guys working here, and a good one is Kirk Merrington. I would bet, when the dust settles, you will have a gun that has been chamber sleeved down to 20 gauge, bummer, but, better than not shooting it.
Sorry to hear of what sounds like a true problem. Good Luck.
Best,
Ted