Fully paid phone been told will be locked forever since moving service to other carrier

Been told by a representative today, my new iPhone 17 I bought from xfinity store which I paid in full will not be refunded or neither be unlocked since I moved my service from Xfinity Mobile to Verizon. They basically wanna force me to go back to xfinity otherwise I will not be able to use the phone. This is the most ridiculous things I have ever heard.