I think, the only response to what you have indicated, is that you 'should' have read the T&Cs on either the voucher or the website ...
But really, if you didn't get to use the voucher 'that' time ( and now you know 'how' it's to be used ) ... just keep it for next time.
Also, if you had of read my post ( on this Forum ) on almost exactly this issue, you would have been forewarned ...
But really, if you didn't get to use the voucher 'that' time ( and now you know 'how' it's to be used ) ... just keep it for next time.
Also, if you had of read my post ( on this Forum ) on almost exactly this issue, you would have been forewarned ...