Apple Rejects Dead Pixel-Related Warranty Claim for iPhone 13

My iPhone 13, purchased on July 18, 2022, developed a dead pixel in the upper right corner of the screen that gradually grew in size exactly one year later. I contacted Apple's authorized partner, Markantalya Troy, about this issue and handed over my phone for warranty repair on July 31, 2023. According to the service response received on 17.08.2023, there was unauthorized activity on the device, and thus it was not covered under warranty. I've never had my device serviced or done anything unauthorized with it before. Furthermore, they damaged the part where the opening screws are located when they opened the device in the service center. When I inquired about the nature of this unauthorized intervention with Apple, they stated that the device did not leave the factory in its original condition.