What do I do about my cat being stolen?

My cat hasn’t been home for a couple of days. She never really leaves the house. The basement is the farthest she goes and she is always here to greet me in the morning. But hasn’t been the past few days. I went to the basement shaking treats because she comes to the sound. I heard her but not in the basement. I heard her in my upstairs nieghbors hallway. when I looked under the door I seen her paws face and collar. I knocked on the door and I heard someone go to the back door and then walk back upstairs. when I knocked again this time louder the person came back and opened the door. when I asked them to give me my cat they said they did not have her. I told them I seen her from under the door. my neighbor then got defensive and slammed the door in my face. I know my nieghbor has my cat but I don’t know what to do. do I call the cops or something? please help. everyone misses her dearly and fear that she might be in danger being up there. due to no food and no water.. PLEASE HELP!!!