Michaelfjs:Lightbox Terms and conditions doesn't explicitly state they will charge you after the voucher has expired
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Uh, you're right it's not explicit, but:
The subscription will automatically renew after the expiry of the trial period, unless you decide to end your subscription before the expiry date.
reasonably means you'll be charged for the non-free period you roll into. Noteably, it does explicitly state you must cancel to not roll over, also nowhere do they imply they'll warn you first.