As you have used the tag Samsung, then unless your set is from before 2016 or is a Serif model, it is highly likely that you have the Now app on your TV, and so may not need a replacement for your box.
If it’s apparently not available on the Smart Hub, look in the Samsung App Store, and see if it is there to download.
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.