What do I do if someone owes me money in a security deposit?

Last November, my old roommate schemed with her best friend to kick me out so he could move in. They fabricated stories about me which spooked my parents into forcing me to give up my lease to her friend (my mother was co-signer on the lease). I signed an agreement for my name to be removed and his taken over. I was released of all payment from then on and was entitled to my security deposit ($500) back. He agreed to pay me the $500 but asked for leniency since he had no job. He is now well off and still won't pay the money. His story has now changed to my money is with the apartment and I won't get it back until their lease is up, therefore my money is still with the apartment. Considering I have no legal binding with that apartment, does his statement stand? If I file a claim with the small claims court, do I have a case? Thank you so much!!