Default Xperia Z Unlocking bootloader issues

hey, this is my first post on here.
A while ago I got my Xperia Z which is unlocked to all networks and I checked in the service menu and it said I could unlock the bootloader so I did so and installed my own roms, then it became faulty so I got it repaired but before so I flashed the stock rom on there just incase it was refused to be repaired because of the custom rom.
When I got it back I discovered in the service menu my bootloader can no longer but unlocked and I cannot root it or put CWM on it or anything as I keep getting errors... any advise?
I tried using the original bootloader unlock code I got but the phone rejects it saying something like 'FAILED remote does not have permission' or something along those lines in the CMD while using the fastboot code.