Xfinity says phone is unlocked but phone is LOCKED

I initially bought an iPhone 13 with xfinity years ago. It became damaged and I used my apple care plan to get a new one. I’ve since paid off the phone and am now looking to switch carriers due to xfinity promising me $500 trade in credit for another phone and then later denying it and only giving me a $280 credit. 
As I am going through the process of changing carriers, my iPhone 13 states carrier lock, sim lock. When calling xfinity they insist that it is unlocked. I have conferenced called with the new carrier who informed them is it NOT UNLOCKED AND Xfinity said there is nothing they can do. I paid $1,300 for a phone I now cannot use. I refuse to continue using Xfinity going forward due to these two instances.

In store they are not able to help me and when I call, they rush me off the phone saying they’ve put in a ticket (which has failed 4 times already) or just hang up on me.

How can I explain to them that my phone is still locked? I have two IMEI numbers but they refuse to try anything different to help me.