BT "Exclusive" Gift Card

I have been sent a BT Exclusive gift card the waives all the set up charges for BT infinity, £30 activation charge, hub postage etc 

I think they have sent me the card because i completed their form to order infinity then cancelled the form at the last minute. Anyway where the hell do you enter the code on the card to get your free set package? The only details are go to: bt.com/serviceinfinity or ring a free-phone number. I don't fancy the phone call so thought id try the website but god knows how you are supposed to enter the code.