@Anonymous User
Welcome to the forum. It could be because you have two different passes active - have a look at your My Account>My Payments page to see what you've been charged for
https://account.nowtv.com/payments
If it doesn't show the second charge it might be coming from another account you have, try checking any other accounts to see if there are active passes there. If you need help sorting it out or getting a refund probably best if you pop onto live chat, explain what's happened and hopefully they will sort it for you. To get to live chat, go to the following help page and choose the live chat option.
https://help.nowtv.com/contact-us/how-do-i-cancel-now-tv
