I agree that it was a bad idea to start work without a contract in place, and I also agree that they don't owe me anything until one is. But note that this is a two-way street: they don't owe me anything without a contract, but neither do they have the right to use my work. Authors generally let that slide, but they are setting themselves up for a world of pain if someone objects. (I did so on the book, and suddenly they had no negotiating leverage.)