Apple iPhone 12 Network And Wi-Fi Problems

My iPhone 12 has a Wi-Fi and network problem. I took it to Genpa technical service, where they tested the device and claimed there was no issue. The Apple solution center couldn't provide a solution either. My device consistently experiences network and Wi-Fi problems. The Türk Telekom operator issued a ticket number and confirmed there were no network problems in the area. Even though my phone displays a full 4.5G signal, callers often say, "You can't be reached, why is your phone turned off?" This happens intermittently throughout the day, despite my device receiving a strong signal. While browsing social media with a full 4.5G connection, I encounter lag, freezing, and loading errors. Technical service and Apple remote support insist there are no issues after running tests. I have screen recordings and evidence, yet Apple has taken no action on the device. My warranty has expired, and they suggested extending it. The device was sent back to Genpa, with no issues found during testing. On the same day, I visited Genpa with a friend whose phone wasn't charging. When we received my device, we tried her charging cable on my phone, and it charged successfully. This raised questions about the phone's problem. We conducted further tests, and the device charged without any issues. It appears that even though the cable and phone were tested separately, they weren't charging each other. This raises doubts about the accuracy of the tests conducted. I believe these issues can be addressed in discussions with Mr. Erdem from Apple's senior department. As a loyal Apple user for ten years, I'm deeply disappointed!