The gum if smeared across a sole needs to be real cold to stay brattle enough to chip off. Within moments of being taken from the fridge I’m sure the gum film lost it’s brittleness. Get a thin bladed screwdriver, a paper towel and and some ice cubes. Grab a cube with the paper towel and press the cube firmly right down on the area you wish to chill for 30 seconds or so them immediately put the screwdriver to it.