how to get a replacement?

I have an iphone 12 pro max with At & t, yesterday The phone stopped reading the sim card, I called at & t and we did several procedures in which it was deduced that my phone is not reading the sim card and they communicated me with apple support; they also deduced that the The problem was the phone but I should still go to an apple store so that a technician would discard everything that we had already tried, as in the area where I live there is no apple store (midland tx) they sent me to bestbuy where according to staff trained, when I come, the technical assumption tells me that everything is fine with the phone that the problem is because my phone was never registered to at & t since when you go to settings and go to cell phone it does not have any information (according to at & t that happens because the phone does not read the sim card and therefore cannot access that menu)

What can I do to get a replacement since my warranty is valid and it is obvious that the problem is the phone (since my sim card works in other phones except mine, nor does the phone read other sim cards)