iPhone 12 Pro Max is dead

My wife was using her iPhone 12 Pro Max until battery percentage to 54%. Then, she charged the phone and checked charging was Ok. One hour later, she checked the phone and found that screen is black. So, I tried to power up by using power button, volume up and down button. But it did not work. Then, I send to Apple authorized service center in Myanmar. Three days later, they replied to me, they cannot find the fault and can't solve. They explained me to replace everything except screen and camera. What should I do. Could you give suggestion.