This happens in Germany.
Work culture doesn’t fit my personality: I don’t talk much, I keep to myself, I simply want to do my job and go home, I separate my personal life from work, my colleagues are full fledged gossips, ignore the duties that need to be done and then expect me to help them when they are late. I don’t have patience for that crap anymore.
Due to internal regulations, I have to stay on the unit for 4 weeks after sending my notice. Answering honestly the question of why I’m quitting would ensure that they yell at me and bully me, and I don’t want to experience that again. Even saying ‘it’s none of your business’ ensures that they feel insulted and start yelling. I have decided I don’t have patience for people like that anymore.
So, what do I say?
At this point OP has already signed a new contract though. Also I’d make up a ridiculous number to sow doubt among the asshats.
But yeah the ‘you could have offered me a raise before to avoid all this’ is a good point.