Locked phone with ghost carrier

I bought an”unlocked” iPhone SE 3rd gen off of offer up. Called my current provider to transfer my number and was told that it was successful and my old phone stopped working. Now I have no phone since the one purchased says no sim, sim locked my old one doesn’t work and when I call my number is now associated with the SE.

I did an IMEI search and xfinity came back as the carrier, contacted them and they could not find the phone with IMEI search, my phone doesn’t say what carrier and apple was contacted and I shared my screen and they also could not figure out the carrier. Why is there not some universal code for this matter or why can’t anyone figure it out? What do I do when my numbers on it and it’s still locked?