If possible remove the opposite axle--sometimes they come out easier.Once its out you should be able to see the axle you started on(inside the rear end).Make sure its pushed all the way into the differential and try to get some oil on what you see.Then use any round steel bar(old axle,rebar,or pipe) and a heavy hammer and knock it out.If any of this fails, there is a more drastic course.Take a slim but wide chisel or a large screwdriver or a prybar and hammer it into the joint between the axle and where it enters the diff.on the forward side of axle.This should slightly "****" the axle.Hit the opposite side with hammer or old axle and it should pop out.I worked in a riding park for years as a mechanic and used this method several times.Don't forget--use plenty of grease on splines when installing new axle.