Had this happen.....ONCE! LOL!
pulled the head (excuse me! RIM.) off a .270 Win case in a RCBS sizing die.
You know what "Cerrosafe" is?
It's a hard, lead like material that has a super low melting point! (less than 200°F)
Remove the decapping set up if possible. Plug die just above case mouth. Fill case with melted Cerrosafe. Give it about 10 minutes to set up, then use a rod to push the case out the bottom of the die.
What I did:
I almost destroyed my stuck case remover! It WOULD NOT budge the stuck case!
It stayed stuck on the die over a year as I pondered a solution. Thank goodness, I had a backup die!
Solution: don't remember what I was doing, but I was filing on the tang of a small, chainsaw sharpening file.
Then it dawns on me, the die is super hard. The file tang is actually mild steel and can be shaped with a file.
I sharpened the file tang to a long angle on one side. An angle steep enough to force the sharpened end between the case and die wall.
THEN....I cut the head off the case and cautiously began driving (tapping?) the sharpened file tang between the case and the die body!
IT WORKED!
I had to cut the case top to bottom (bottom to top?) twice....and the case popped right out!
I have used that particular .270 die to resize 0robably thousand of .270 cases since. No ill effects!