First, welcome to the site.
You say "we were promised". Hopefully, that promise was made directly by the guy running things, either verbal or written.
Assuming so, the first move would be to have a civilized face-to-face with him and discuss your grievances. If he's an upstanding guy and you have all your facts straight, you two should be able to come to a fair resolution (pro-rated, future credit, etc.) Maybe there are valid reasons for the differences.
If that doesn't work out, things become much more tricky. Remember, the baseball world is a small one and pretty well connected. Be sure you want to burn that bridge before doing so. In fact, by stating your town, the exact fee and schedule details, you probably already threw out more info than you should have, considering you have labeled the team as corrupt.
If the bridge is worth burning, there's legal action, active word-of-mouth campaign or dropping a burning poop bag on his front door
Sorry. Seriously, my son is a 2012 and has been involved with several club teams with various sports and I have coached some club teams. Just recently, I had our first situation where I had to have such a discussion and was able to work out a fair resolution financially. Unfortunately, you're not able to do anything about getting the season back. Do your homework when signing up. It's a slippery slope. You don't want to be the difficult dad but you want to make sure you and your son make the right decisions with joining such club teams.
Best of luck.