Try this: Go to Settings > General > Reset > Reset Network Settings. Nothing is lost except all internet data. Just make sure you have any Wi-Fi passwords handy because you'll have to type them again. Good luck!
- Reset the iOS device. Nothing will be lost
Reset iOS device: Hold down the On/Off button and the Home button at the same time for at
least ten seconds, until the Apple logo appears.
- Power off and then back on the router
- Reset network settings: Settings>General>Reset>Reset Network Settings
- Restore from backup. See:
- Restore to factory settings/new iOS device.
- Make an appointment at the Genius Bar of an Apple store.