@Aadam
You need to make sure that the account you are logging in to is the one you added your payment details to.
If you have checked that this is the case, you need to talk to Now on Live Chat to get this resolved:-
https://help.nowtv.com/article/how-to-contact-now
From here, you can contact Now via Live Chat.
Avoid ‘Get Help Quickly’ if you have come to this screen. This leads to the Nowbot, an AI bot that would assist you in navigating the Help very nicely; but if you are here, you have already gone beyond that.
Set a Payment PIN on your account so that no-one but you can buy memberships on it. Check your bank accounts monthly for any other unexpected payments to Now. That way you can at least nip them in the bud, while you and Now figure out whose fault they are.