My question involves labor and employment law for the state of: New York, New York

Back in May 5 2010 I was falsely accused of stealing. I was never questioned nor asked if it was true. My employer just stated that I couldn't be a cashier, or relieve any other cashier for lunch. 2 years has pasted and I was again giving the opportunity to regain overtime and due to fact that cashiers were needed. But on Friday the 21 of 2012, under new management this incident was mentioned again causing me to lose my overtime and again banding me from come in side the cashiers booth. What I don't understand is, If my union and labor relations came to an agreement; that their wasn't enough evidence to convict or prosecute me for that accusation. Why is it still being applied now AGAIN?! ***It's way more to it, but this is basically the icing on the cake.....I believe I am a victim of Defamation of Character were they are slandering my reputation, and they are treating me like a criminal were I was never giving a chance to defend my self. This where the Presumption of my innocence comes into play because I was never found GUILTY!! HELP!! what should I do?!