I've used many different products thru the years for stripping paint from styrene. The two that I found works best for me is brake fluid and Super Clean. I left an old gluebomb JoHan Dodge body in brake fluid for around two weeks due to the fact that it had a coat of paint thicker than the plastic itself! The paint finally turned loose, and the plastic didn't suffer any.
I once tried oven cleaner on a TESTORS paint job, and it didn't work for me. So that one went into the brake fluid, too.
Nowadays, I use Super Clean, as I find it a bit less messy to clean up than brake fluid.