Go on the live Chat, and explain. If you have a good enough reason, they will override the restriction temporarily for you.
Personally, I think unused device swaps should roll over from month to month, up to a maximum of four.
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.