"Unfortunately your existing iPhone subscription is managed by Apple, and we cannot therefore discount this cost for you. However, if you would like to subscribe to a new Guardian subscription pack, we would be happy to credit your account with the difference in costs for your remaining subscription, once this has expired. Please call us on 0844 543 8005, 9am to 5pm Monday to Friday. All calls are charged at a local rate."

http://www.guardian.co.uk/subscriber-direct/subscription-frequently-asked-questions?newsfeed=true

Drop the Advertising Standards Authority a note.

They can and will take action against this "misleading or false price indication".