If none of the solutions worked, you have to factory reset it. You can do this from the recovery option feature available for phone. There isn't an exact method to access recovery mode, but users found that one of the following methods will get you to Recovery Mode. After you access this mode, use Wipe Data/Factory Reset and the phone should be restored to factory condition.
- Power + Volume Down
- Power + Volume Up
- Power + Home + Volume up + Volume down