Unplug the Stick and wait until it is cool.
Plug it back in, and hold in the little button on the side of the Stick for over 15 seconds, so that it Factory Resets.
Set it up again, and then try again,
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.