If you go to Manage permissions which is in the “My Account” area (www.bt.com/business/myaccount) and with logging in with your account number you'll see a link to “Become Admin”. Simply click on this and a PIN will be sent in the post to your Finance department at the billing address which you will need to input. You'll see a link at the top of the Manage permissions page to “Unlock PIN” after you've requested it. The PIN will last 28 days unless you request another.
If you still need help please come back here and I can look into this further.
^AimieG - Community Moderator