It’s FILL-uh-steen in American English; I always thought that was the only correct way to say it.
But it’s FILL-uh-styne in British English. That used to grate on my last nerve when I heard it in movies and on TV. (This includes my beloved “Hannibal” in 2000.)
But I’m the ****-up in this equation and I need to chill. (And I am arguably a Philistine here.)