There is a trick to using less force on your puller to remove a stubborn crankarm, even if you have a proper tool.

Apply the wrench force to the puller, than straddle the bike and apply weight to the pedals with the crankarms horizontal.
Flip the cranks a few times so as to reverse the torsion loading on the square tapers.

You'll have to repeat the tightening perhaps several times, as each application of wrench force and crank torsion finally creeps the arms off of the spindle.

I am suspicious of the plastic part though, not sure it can sustain the pressure without promptly losing pushing force.
So, if you can get a helper to tighten your bolt while you dance on the pedals, maybe the arm loosens faster.
Oh, and it helps if you're heavy, or if you can apply a downward impact load on the pedals, helps twist the taper more.
And of course a penetrant will also help.