Brake Caliper Piston will not compress?

What are you using for penetrating oil on it? Have you tried something like PB Blaster or Liquid Wrench? I use PB Blaster, which is a very strong penetrating oil. I will look for some other methods but tapping it out is how I've always done it.
There are other methods we would use in extreme situations in a shop, but it involves using heat. But if you have never worked with a torch on vehicles before I don't recommend that. Is it possible to get the edge of a large U clamp on the section of cable housing that is sticking out there? And possibly put pressure on it that way.