My Ex Took My Cat Along Side My Other Items And Wont Let Me Get Them Back

So my ex and i recently broke up and we would not let me have my cat back alongside some other expensive stuff that i own and paperwork left behind. He and i live on different states but i moved to his state when i found out i was pregnant. I moved with my cat, had the baby, and lived with him and his parents for a year paying $400 rent to stay with him in his room. I had no choice since i was away from home at that point. After an argument, he told me to leave in the middle of the night with the baby so i was not able to grab my cat with me. I know no one in his state and have no where to go but back to where i used to live which is across the country. My ex refused to talk to me and settle things. He blocked me and had his mom and step dad do all the communication for him. Since they only know his side of the story, they would not cooperate and give me my items and told me to stop harassing them or they will go to the police. How do i get my cat back? Ive had her since she was a kitten and she is my baby.