Who stole my iPhone ? It was a trade in.

I went into Xfinity mobile on September 12, 2025 to get a new phone. The rep and I agreed that he would trade in my iPhone 13 Pro Max for a credit and then I would receive a iPhone 15 Pro Max. I notice that I haven’t received any emails or documents pertaining to the trade in and also my bill begin to rise. So, I  visit a store on Saturday, December 6, 2025 and I speak to rep. I’m asked did I purchases a device and then return it. No, I did not. I came over to Xfinity from another carrier with my iPhone 13 Pro Max. They couldn’t give me any information. So, I had to go to the original store I purchase from at this point.  I was told that there is no paper trail on my phone and that no one in the store knows what happens to it. Also, my phone was processed as an upgrade instead of a trade in. Oh, I should be happy I still got a credit. I’m constantly speaking to a rep and still have yet to speak directly to a manager. Unprofessional. They are no help and keep telling me that the rep that did my phone no longer works there. Not my problem. So, did someone steal my iPhone 13 Pro Max? Where is my phone and who stole it? It never made it to the trade in department.