Silence ALL sounds

Guys, I'm pulling what little hair I have out. What part of ALL sounds doesn't GOOGLE get??? Recently I muted my phone, in a movie theater, only to have a game IGNORE my sounds settings._( I unistalled it!!).......and then another time I had YOUTUBE do the SAME thing.......what part of SILENCE doesn't GOOGLE understand?? I'm running STOCK Lollipop 5.0 with latest update. Any ideas??