Wow. That's tough. If a working demo doesn't convince them, I'm not sure what will. "See this? Do you want this?" is a pretty simple question. Do they need more evidence of unit- and integration testing? Do they need some/more user feedback before proceeding?

Remember, some people don't listen to reason, some of your wise seed will fall on rocky ground, and don't try to teach a pig to sing. I'll stop now :-) Best of luck again.