At this point only 2 options remain:
Take your iPhone to an Apple store or other Apple authorized service location to have this issue diagnosed.
or
Restore your iPhone:
- Backup of your device to iCloud or iTunes: https://support.apple.com/en-ca/HT203977
- Then try to reset the device: Settings → General → Reset → Reset All Settings
- If that doesn't work, then Erase your device: Settings → General → Reset → Erase All Content and Settings
- Then restore your device: https://support.apple.com/en-ca/HT204184