I did this and i lost all my software and firmware updates also, now I don't have any idea how to get firmware update when i lost it and tried all possible things and searches but nothing is helpful till yet!
Firmware could not have been rolled back by hard reset or restoring, just not possible, unless you flashed your phone with older ROM with NCS.
If you phone was successfully update to GDR2/Amber then your firmware should read settings->about->more info
OS Version should read 8.0.10328.78 and firmware revision 3046.0000.1328.2024. If you have that then you have GDR2/Amber.
You just need to most likely update all the individual Nokia System Apps (Extras, Access Point, Audio, Display,etc). Do not install Glance, does not work with 521.
download and install the SysAppPusher and manually install System Apps and Apps has needed. Once again do not install glance does not work with 521.
If the OS Version / Firmware do not read that, then use Wifi and use phone update to update phone. If does not work then you will need to use Nokia Care Suite or Nokia Software Update to flash to current version.
You will still have to run sysapp pusher and manually update the Nokia System App's and other Nokia Apps.
SysApp Pusher