Go into your account settings and start Cancelling the Cinema membership. You may find that Now agree with you about the VFM, and will offer you a reduced price deal to stay 😛
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.