They funded me at the start a lump sum to build the demo, and then there was a vague promise to send me some more once I delivered so that I could continue work

They funded me at the start a lump sum to build the demo, and then there was a vague promise to send me some more once I delivered so that I could continue working while we pitch it to investors. The thing that's not working for me is the vague promise and the fact that I feel like a student who was put on a team project and left to do it alone. Throughout I was told that they like the results, so I kept working on it without finding other sources of income. Apologies for being all over the place, I'm not in the best mental state and it's a long story (to me at least).