Company Standard Practices

I recently quit a job that I have had for 2 years. I left on excellent terms and had my best sales month ever. The company paid my base salary but refeuses to pay my commissions for the final month sales. In the employment agreement it does say in fine print that they would not pay commission for the final month. However, over the last year all 6 reps that were either fired or quit were paid their last commission amount including one female rep that quit the same month I did and was paid her commission. The explanation was that she was great for business and helped create a smooth transition. I have better sales statistics and I even worked one extra day after my last day helping them transition a new employee. Do I have a case here? This seems like discrimination to me.