Persistent iPhone 11 Device Issues: 3 Service Visits, No Connection

I gave my device for repair 2 times and 1 time to Vatan Bilgisayar, the place where I bought it. I have Bluetooth and Wi-Fi disconnection problems on my device. When I first gave it to them, the screen was changed and my intact screen started to not print. I gave it again and the screen problem was solved, but the Wi-Fi and Bluetooth problem continued. For the 3rd time, I gave it to Vatan Bilgisayar and they sent it to the authorized service KVK and they cleaned the speaker and the charging socket. But there is no result, unfortunately my problem continues in the same way. When I contacted the Apple center, they made me back up from the computer and reinstall it again. The problem still continues, 3 visits to service, nothing yet!