What can I do with this problem?

Try the following in order: (Note: If any step resolves the issue, STOP, do not go on to the next step.)

• Power the iOS device OFF, then ON.
• Restart your iOS device: To restart your (perform a soft reset) iOS device, press and hold the sleep/wake button while pressing and holding the Home button. When you see the Apple logo, release both buttons. (Note: This will NOT delete any data or apps, nor change any of its settings.)
• Toggle Airplane Mode OFF, then ON.
• Reset your iOS device's Wi-Fi settings: Settings > General > Reset > Reset Network Settings
• Perform a "Reset All Settings" reset: Settings > General > Reset > Reset All Settings
• Reset your iOS device to its factory default settings: Settings > General > Reset > Erase All Content and Settings (Note: The following willerase all of your data and media and resets all of the iOS device's settings. You will need to restore it from a previous backup from either iTunes or iCloud.)
• Make aGenius Bar appointmentat your local Apple Store or take it to anApple Authorized Service Provider.

Did you also complete the last step and take it to your local Apple Store?

Make sure your iPhone is up to date.

Update your iPhone, iPad, or iPod touch - Apple Support

... then I guess you haven't tried everything that I provided you.