Assuming you live in the U.S., whenever you create something and put it in a permanent form it is automatically copyrighted.

The threat of the cease and desist is the catalyst for getting paid. You really are going to need to brush up on copyright law, however, because if it looks like you don't know what you're talking about, this whole thing will fail.

Your only other move is to grovel and beg them for money after the fact.

If you're hungry, there should be a number of food banks that will help you in your area.