They have to pay you what the employment contract specifies, unless there's a clause saying it doesn't kick in for 4 weeks. I don't know your state, so you get the generic answer:
Check your state's labor laws on back wages owed and commissions earned but unpaid. Also check the lien laws - you may be able to record a lien aganist the dealership (and perhaps its inventory). If you do, the dealer will have to get a lien release that he can record (to clear title). This is how you get the dealer to pay for the costs of researching lien laws and drafting and recording your lien.
Talk to the dealer and let him know that you know your rights and WILL take strong action. He'll back down and issue a check. Double check his math. He sounds like a shyster.
You could also picket across the entrance to his lot with a big sign saying "XYZ Mazda Bilks Workers" and hand out leaflets telling your story to all who stop by. (Make certain everything you say is absolutely, 100% true and that you can document it.) Just imagine the publicity when the papers take your picture and run it on the front of section B......
Good luck.
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This is not legal advice and you are not my client. Double check everything with your own attorney and your state's laws.