@Anonymous User
You do. Look under the various headings under My Account, notably Broadband & calls, Orders & appointments, and Message centre.
The number you should call (which can be different for different people, I understand) will be found under one or more of these headings.
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.
