@Archie
if you are getting Netflix via Sky, and it is cheaper than direct, or it is mandatory that you take it from Sky, or it is an indissoluble part of a bundle you want, then yes.
Or any other reason that would have you paying twice for the same thing, really.
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.
