To erase yourself completely, try the advice here:-
Nobody has come back lately and said it didn’t work for them, anyway. But if the person who answers says it’s for Sky only, refer them to the link, remind them of their GDPR obligations, and politely but firmly insist.
So please ‘Accept Answer’ now, if you are so inclined, as you won’t be able to come back and do it later
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.