iphone 6 shut down suddenly

I bought an iPhone 6S two and a half years ago and the other day it just shut down and wont turn back on, it's completely dead. I looked on the apple website and it seems that iPhone 6S and pro had manufacturing problems during 2018 and 2019. I bought my phone in 2019 and most probably this is the cause of the problem because I have done nothing to harm the phone. I went to the genius bar and they said nothing is wrong with the battery or outside of the phone. My phone is 5 months out of the guarantee and I asked apple over the phone to make an exception as it was not my fault and they would not. It makes me feel like I really do not trust apple as the phone is not even 3 years old. What can I do?