From their email response its looks like they cancelled you entierly and your not even getting half because you questioned them. If you are still doing the breaks I'd do as above-do as little as possible. Probably the best thing to do is walk away and not be available when they need some volunteer work. In my situation over the years I've had a bad habit of not doing signed contracts but did learn something interesting. Twice I was cancelled last minute for month long restaurant gigs in places I had worked on a steady basis. Both times I only found out when I called to see if it was possible for me to set up early in the afternoon. "Oh we got a DJ" and "Oh we forgot" . That killed a whole month for me so I pursued them thru a lawyer friend. The law says that if you conducted previous business with them via a verbal contract then any ongoing verbal contracts are legal. I won both cases and got paid in full. I've also got the "we found someone cheaper" after being promised a date and that was from a Country Club board member. I just walked.
Your right, people today have less ethics so be careful and good luck.