Why did my phone heat up and stopped working

Hello, I bought my i phone 11 pro about a year and half ago and I have not dropped it or even scratched it a bit. It is purely in new condition but yesterday it just heated up and stopped working. I took it to the retailer from whomI bought the phone but they said everything is good inside and seems like the logic board it gone. It is really frustrating as I paid almost $1500 for it. and they have asked me to pay $850 more in exchange for another one. Yes that is the price for iPhones in Nepal. Please help if there are other options or something they aren’t able to see.