Thanks for your post, and a big welcome to the Community Forums!
We would have sent you an email with the security key on at the time of taking out the handset. We'd recommend having a wiz through your emails and searching the words 'Credit Agreement' or 'security key' and you should be able to find it.
If not, give us a shout and we'll be happy to assist further.
No problem, thanks for getting back to us.
I'll pop you over a private message now so I can get the details resent out to you.
Please look out for my message over at the purple envelope icon.