Since you've already committed to not working with the company again, why not call the highest contact you have and, in as pleasant a manner as you can muster, politely request payment for services rendered? If it were me, it would go something like this: "Hi ____, how are you?. I understand you've decided to implement the _______ project internally, based on the spec I wrote. I'm really glad it met your needs and I…
i try to go down that track now - decided to bill them for business analysis and see how things turn out ... i'll report here :-)
billing only for the hours would be under value i think, i simply see it as a business analysis and even offer them to give them deeper insight in their own business if desired - simply change the seats ... lets see.