@Louis
Adding to what @gavs82008 said, it would take just over a month for you to be charged twice on a single free trial, and these only ever lasted a week.
Did you perhaps stay from one membership, such as Entertainment, into another, such as Cinema, which would certainly get you charged twice within a couple of days or so?
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.
