Problems with Free 1 year subscription to Apple TV

I've just purchased a new iMac and I'm having problems accessing the free 1 year subscription to Apple TV+. When I go in to Apple TV+ it just shows a free 7 days trial rather then the 1 year subscription. I've tried logging in and out of my Apple ID but that hasn't solved the problem.

Does any body have any ideas of how I can fix this problem?