Put the mpc in a vise and twist the trumpet until the lead pipe twists and/or breaks. Then take it to the repair guy to have the lead pipe replaced, and they can just cut the mpc out of the wreckage.

At least that is the method three trumpet player dads (actually two dads and one mom) used during my career.

In seriousness, the method described below works and is what I have seen repair guys do. Tighten the puller, tap the pipe with a rawhide mallet. Another slight turn, tap tap tap. If you are able to heat it up a little it helps, but be careful to not do it too much or you might melt the solder of the mpc receiver.