You found the option and tried turning it off and on?
I will second the advise to reset the phone. There are several different levels of reset depending on how long you hold the power key down. I think the most serious of them is at 31 seconds or thereabouts.
If that doesn't work, you can try a factory reset My phone had a lot of weird glitchy behavior that all went away when I did a factory reset, for what it is worth. . That will wipe everything off your phone, of course, and is a nuisance. But if you have stored your contacts and whatnot with Google, it's not nearly as bad as in the old days. And I was pleasantly surprised to find that the SD card (under Lollipop, but probably still true under Marshmallow if you have it set up as external memory) wasn't affected, so I didn't have to re-copy my photos and music to the phone. Mostly I just had to restore what apps I put where on the home screen.