Trade in returned

I traded in my iPhone XR in January for $350 credit towards my new phone. Today, June 13th, I got it back in the mail with no explanation. After reading some of these posts, it appears this is all a scam and my phone was never going to be accepted??? You have to be kidding me. I would have never bought this new phone if I wouldn’t have received a credit. The phone was old, they obviously knew that. But it worked great and looked great. I just joined mobile and now I’m already planning on leaving. Some of the worst customer service ever! I cannot believe this!