had the same issue, this is what i done
i had the same problem, i flashed my phone with a cooked rom then tried to unlock it and it would not bring up the sim locked screen, i tried for hours and then i thought if i reflashed the phone with the original uk orange rom then this must work??? i flashed the rom and as soon as i put a none orange sim in the unlock request popped up, i then entered my unlock code and the phone unlocked straight away. i then reflashed with a cooked rom from here and all is well, phone unlocked and debranded YERRRRRRRRRR!!!!!!!! anymore advice needed then just PM me, many thanks to this forum and the people who reply to threads...................