Apple iPhone 15 Return Problem Unresolved

The iPhone 15 I bought turned out to be faulty. I contacted Apple support multiple times, but they couldn't find any problem. They directed me to a service center. I went to Troy service in Mavibahçe three times, each time a different issue came up, and I couldn't manage to hand it over. I called customer service numerous times, but nothing changed. Finally, I went to the place where I bought it, and they handed it over today. It's been about five months since I bought the brand new iPhone 15, and since I got it, my calls and internet connection keep getting cut off. Despite this, iPhone didn't agree to replace it, and we're currently at the service stage.