
Difficult one! I assume the brandy does not need to be saved, (given you have already tried oil) but that the decanter does.
Do your kitchen worktops have a wooden edge - or do you have a table with a wooden edge? Sometimes, tapping the stopper
very gently all around on a "soft" edge (such as wood) can loosen it.
Did the olive oil seep between the sides of the stopper and the neck of the decanter?