As an interim, short-term move, what do you think of the idea of looking for a more agreeable client with whom to do similar work?
You don’t even have to make a final decision on it. But you could do something like put up an ad or a post on some relevant website that describes your experience and says you’re willing to discuss offers. Then you’re free to reject any callers if you don’t like them or if you don’t yet want to change the current situation.
It’s possible that with all of the experience you now have, you’d be much better able to assess and evaluate potential clients than you were when you signed on for this current client.