Port Authorisation Code (PAC)... Muppet!
The last [residential] customer phones to need a PAC code were the HTC 620/710.
Succesive handsets for BTBB Anywhere were/are unlocked to network and contain no BT software on them.
I guessed so.
Anyway, if you contact the mods in my link they should be able to help you. I had a billing problem (not as big as yours) and the Indian call centre kept telling me it was sorted out for a couple of months, but nothing happened - then 1 mail to the mods and a mail and call back and it was sorted in a couple of days.