Criminal tresping?

My sis is incarcerated and she has given me her keys so that I may look after her place during her incarceration. The police saw me in the building going toward the exit and said I was tresping though I had her keys and her permission to be there. They took her keys from me, left it in the property manager's office and told me that I was being placed on a banned list, which in the state of IL they can't do unless they prove tresp in court and get an injunction from the judge. So, what are the proper steps for me to take if I want to go to court for them restricting me and my sister of our rights. Because no matter if she's there or not, I was given permission to be there, her keys are the proof and in court she can prove, even the paper that the police wrote said that I had her keys. I had a right to be there and the reason is a good reason. The main reason for the ban list is to reduce possible crime from occurring. I have committed no crime as a guest of my sister.