Contact Live Chat and explain.
If you have not used the Pass, which they can check, they are the people you can ask for a refund.
And you need to ensure the Pass is Cancelled, so this does not happen to you again next month.
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.
If you take an offer that comes with a ‘free trial’ of Boost or another Membership, Cancel them straight away. You will still get the full duration of the trial, and if you decide you do want to continue with one or another of the trial products, just revisit the Cancel, and UnCancel it.