Are you sure the diff is not sat on an angle in your gearbox? As i know some diff need shimming! Could be why the shaft isnt comeing out! just a thought If you could get someone to wiggle the cup why you give it a good old smash with a hammer from other side of the gearbox it might come If you cut it out the shaft is still going to be left inside the diff and will be alot hard to get out as you wont have nothing to hit1 Edit but then again if you did cut it you can still hit it from the other side of the diff