Former Employer Came To My Current Job And Told Them A Reasoning For My Trespass

So I work in the mall and was told today from my current store manager that my old employer is trespassing me. Their reasoning is i was causing a disturbance and was threatening the store manger and employees. This is the weird part they made it seem like I was by myself when I did those supposed action. The only time I been in that store since I quit was with a friend who was also a former employee there and her kid so I have witnesses of me not doing no such things. If I can't fight the trespassing can I get them for defamation? This is a weird situation I have never been in before and all my former and current employers have a hard time believing this "reasoning" I need advice.