spray some PB Blaster or other penetrating oil onto the shaft/nut, let it sit overnight, then if you can put some heat onto the shaft/nut & some more penetrating oil (the hot parts will help draw the oil into the threads).
Now once you've got the puller on the wheel again & tension on everything, & the puller shaft is lined up with the steering shaft, hit the end of the puller thats pushing down on the shaft with a good size hammer, that should pop it loose.