Twiny

Tried this a couple of times on my montefeltro using a heat gun for ten to fifteen minutes receiver was too hot to touch and glue was smoking but can't get the tube to budge! Resorted to bringing the monte to a gunsmith who used a torch on the tube and said he gave it a good heating and couldn't get it to move, was in contact with Benelli who say it should come off anyone encounter this problem?