Try starting up the phone in "Safe Mode" and see if the camera will work. If not, then you probably have a hardware issue. If it does work in "Safe Mode" then there is either a virus, malware or a bad app on the device that is causing the camera issue. Yes, I read that you did resets, but sometimes that doesn't resolve those issues, and definitely not if it is a hardware issue.
To get into "Safe Mode" please do the following.
1. First turn off the phone.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.