Holy crap, an extra 40 hours/week for a whopping $4K/year? WHY WOULD ANYONE WANT TO DO THIS WHY WHY WHYYYYYY? I mean, if you took those 40 hours and got a second job at minimum wage that would be $16,640/year, at least in my state.

Their expectations are insane and abuse. Good for you for telling them to shove it (politely enough to revert to your old position).