you get the occasional jerk client in any business. just with fashion and creative industries it seems that the rear ends are stupider than that of others.
you just have to deal with it and keep going. If they've breached a written agreement then it's easy to walk away and leave them to bother someone else.
don't look at your client's reputation or circumstance though. the only thing that matters is the way they treat you and the way they pay you. if there's no balance between those then cut your losses and leave.
this goes for anyone starting out in this business from models and MUAs to ad agents and PAs