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You might want to check the accesibility settings. That's probably where the problem is coming from.
Best regards,Mikey. For any more questions,PM me. I hope you found what you were looking for.
Sent from my Samsung Galaxy S7 Edge SM-G935F.
I seem to recall BlackBerry having a settings like this, but I was not aware of it being on any other phones. Could be part of a ROM either from a 3rd party OR from the manufacturer. My OnePlus Three does NOT have this settings under accessibility, call settings, OR sound/notification settings, BUT these are the 3 places to look. Perhaps your phone DOES.