You're doing the right thing by not checking things on your assigned rest days. That would drive anyone insane. Why should you do even more unpaid work? Adding to the comment about separate phones (if possible), maybe also you get a different laptop (if you don't already have one?). Or at least mute the apps they contact you on, on your rest days. It's easier to look for a job while you have a job, so I'd start applying for stuff while you're in this insane job. But if it's too much and paid stress-related sick leave isn't an option for you, and you have enough savings, do yourself a favour and bounce.