Refused my commission check

I was working for a collection attorney where the pay was based on a small salary plus commission. The commission was basically the larger portion of my total pay. I worked the whole month of June and basically walked out on July 10th due to my manager's abusive behavior. The attorney my owner told me I was going to get my commission a week later. I called repeatedly and was finally told that I wasn't going to get my check since it was industry standard since I quit. I am owed $4,000 in commission for month of June and feel I am entitled to it since I worked the whole month and that is the incentive of this type of position. What are your feelings fellow forum members??? I am sick over this since and I have worked for several collection attorneys and this has never happened when I left after completing the month