Hi @Anonymous User
A bit of a long shot, double check that your bank card details are up to date by going to the My Account section on here.
Are you having problems accessing any other of your playback devices (if applicable).
Are you using a Sky ID account or nowtv username or email address when attempting to sign into your nowtv box.
Maybe if you are still struggling try nowtv live chat on the link below for further assistance.
https://help.nowtv.com/contact-us/managing-my-devices
