Are you sure the puller and the crank are a match? there are different pullers for square taper and other for splines look at the end of the puller and see if it is the right size to clear the sides around the spindle end and contact just the end of the spindle); also as said before make sure you have removed any washers. Did you try the puller more than once? If not there still may be enough threads to pull the crank (making sure its the right puller). This time tighten the puller with a wrench so you know it has bottomed out.