Traded in iPhone at store did not get a new phone

I went into the store to do a trade in and get a new phone. The store made me trade in my device on site. I still have not received a new phone in the mail as promised. Have called customer service multiple times and nothing. I went back into the store to get my old phone back and was told it was Xfinity property and it would be stealing if I took it back. They even threatened to call the police on me? At this point they just robbed me what can I do now?