Is the window you are trying to get the paint off from stained glass too?
Or just a regular clear window?
If it is just a clear glass window then use a razor blade to remove the paint

Is it that "Gallery Glass" paint that makes windows look like stained glass? Razor blade doesn't work. I've tried. I wish someone would figure this out, my mom painted all her accent windows with this stuff and it looks tacky now 10 years later.

A razor blade and lead trimming tool should do the trick. It creates a film as best I can remember if its really stuck try to get a corner loose and get some kind of oil under it. It will work its way under and should come off.

I've been trying to get it off for two years. Nothing gets it off. I've gotten a tiny corner off in two years. It's ugly and I cannot get it with razor. Any type of goo remover or heat. It is on my door side lights and door window.

In case you haven't figured this out, I just tried this method and it works great

https://www.hunker.com/12001089/how-to-remove-stained-glass-paint-from-windows