Get some dry ice and pack the inside of the tube.Next, take a heat gun or hair dryer and heat the outside of the barrel. The tube should come right out. Clean well and reinstall with anti-size.
I would apply heat, followed by Kroil (or PB Blaster), then try your (correct) wrench, again.
If that doesn't work, it can be bored out by a competent gunsmith or machinist. It's really not that difficult, if you have a lathe with enough clearance in the headstock, or bed length.
I second or is it third the application of PB however I have used the alternating heat/cold cycle with PB to free choke tubes in the past.
What I do is spray some PB on both ends of the choke, let it sit for 10, heat the barrel up with a hair dryer, squirt a bit more PB then put the barrel in the freezer, repeat a few times. The alternating heat/cold cycles expand and contract the steel drawing the PB down between the barrel and choke dissolving the rust.
When I put them back together I use nickle never seize. Never had an issue with chokes using never seize on the threads.
I have never tore down my turkey gun (Rem. 870 supermag), i've had it for about six years. It only gets shot 4 or 5 times a year. I wipe the outside down good after each use. I know it's probably not the best for it. I guess its probably due for a good once over.
I will clean my Rem.1100 after an afternoon of shooting dove though.