Hi
I am assuming that the troublesome joint is between the hose and the tank?
If it hasn't been removed for a long while it is possible the rubber will have adhered to the metal filler neck. It may be possible to break this bond with very careful twisting , but I am guessing that you will have already tried this. You don't want to be using too much force or you will likely weaken the solder flange between the filler neck and the tank surface.
I suspect that heat will make things worse by softening the rubber and increasing the bond between it and the metal.
If you can obtain a spare hose then I have a feeling that the best method may be to make small vertical cuts in the hose until you can actually prise off a strip , this may enable you to twist the rest off , or you may need to continue the process until it does release. Of course this will destroy your hose, but at least you should be able to replace it with the new item.
Good luck
