Any other agents get burned by a real estate "team?"

[Avery Carl]

My real estate investing started going well enough last year for me to quit my corporate job, yay! I already had my real estate license for my own investing purposes, but I do a lot of agent work with my investment connections.  I work for Keller Williams, and was recommended for a high production team within the company because I had been doing so well.

Let me preface with I never wanted to join a team, but I wanted to see what it was like and oh did they promise me the world!  So I joined. Fast forward 2 weeks and I have already gotten off the team because it's just driving to the office to make cold calls. Not why I quit my corporate job! 

Yesterday I had a closing and today I was hit with an email that I owe them a commission split on deals I had under contract from BEFORE I joined the team.  I'm not sure if there's any way I can fight this since I signed a contract, but the agreement dates on the deals are from a week before the contract date, and they are taking a hefty amount of money.  Needless to say, I am furious.  This is an expensive learning experience.  Just wanted to see if any other agents out there had problems like this, and if you have any advice for how to fight it, although I know it's probably a losing battle.