@Anonymous User
Welcome to the forum.
As you didn't cancel the pass in enough time to stop the auto-renew it would be at the discretion of NOW TV whether they give you a refund or not. I'd suggest popping onto live chat, explain what happened and see if they would be willing to refund you as a courtesy.
To get to live chat, go to the following help page and click the Start Live Chat button.
http://help.nowtv.com/contact-us/How-to-cancel-NOW-TV
For future ref you can cancel a pass at any time to stop it auto-renewing and you will still be able to carry on watching for the full month (you can even cancel it as soon as you've applied a voucher code so you don't have to worry about forgetting to do it later).
