Palm Pre Plus unlocking

Hi, I purchased a brand new Palm Pre Plus, which was sold to me from Australia UN-LOCKED (supposedly) however I can't get past the first green screen which asks for a code number. I have been to the two mobile providers where I live and they have no idea and say it is not a network lock, I never lock my sim card, so it can't be that, though just to be certain, I tried different unlocked sim cards. I contacted the supplier I purchsed the phone from and they are still saying the phone was unlocked. I am living overseas right now and really didn't want to post the phone back to the supplier, but I am now thinking it maybe the only way. That is of course unless someone has an idea for me here.
Thanks Christie