I'm lost but here are a few things to try anyway:
Don't both going into Settings. Simply pull down from the top of the screen. From there you can (hopefully) enable Flight Mode just by tapping the aeroplane symbol. Alternatively tapping the loudspeaker symbol twice turns the sound off. (Tapping it just once only takes you into Vibrate Mode).
You can also use the 'Do Not Disturb' function. You can access it via Settings > Notifications. (Alternatively, pull down from the top of the screen, then tap and hold the speaker icon. 'Do Not Disturb' is at the bottom of the page, under 'Looking for something else?').