Live Chat can do this for you. 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
Its a real shame to hear you are leaving NOW TV! But don't worry, if in the future you'd like to re-activate your pass, it can be done as quick as cancelling! Here's a list of steps for cancelling a NOW TV pass:
Select My Account and then Passes & Vouchers You might need to enter your username and password.
Select Cancel Pass next to the pass you would like to cancel, and follow the onscreen steps.
Once your pass is cancelled you’ll see the confirmation message below, and you will get a confirmation email within three hours:
You’ll be able to keep watching until the date your next payment was due. If you are on a NOW TV pre-paid offer, your pass will carry on until its expiration date.
Just a quick tip, if you have other passes on your account you’ll need to cancel each of them individually. Oh, and you can only cancel Sports Day and Week Passes that have been bought in the last 14 days and not activated.
Thanks for getting in touch, not great that it's down to cancelling but I guess I can still help 🙂 Keep an eye out for an e-mail.
NOW TV Team
You can cancel passes using My Account then My Passes
To fully cancel you'll need to visit LIVE CHAT
http://help.nowtv.com/article/How-to-cancel-NOW-TV and click Contact Us - blue box bottom left
Thanks for posting, to add to @Osculogic steps, if you do have a 3 month, 2 month voucher etc. Please make sure you cancel the auto renew when you're in the last month of the pass to get the full entitlement. If you cancel before you will only be able to watch until the end of that month expiration date and lose the remainder
NOW TV Team