Thanks for your post and welcome to the forum. You need to head to Live Chat to sort this. Click on this link http://help.nowtv.com/article/None-of-the-above and hit the Contact Us box on the left of the page, this will take you to the Live Chat & Email options (8am - Midnight).
Hope this helps
Incidentally, NowTV would retain more subscribers if they allowed us to delete the payment details when not required for a purchase. In the current cyber-risk environment, most of us are wary of online fraud and data leaks. You lose a hell of a lot of goodwill by appearing to be deceitful and untrustworthy by not allowing the deletion.