I just ordered through a website with a voucher code. The discounted amount showed up, I paid with my card, and then the full amount was charged to the card.
I called up and apparently their processes don't allow the discount to be applied after the event. They are aware of 'lots of glitches' on their website, which has been newly designed.
I'm really cross. To my mind, this is fraud. If they know the website is doing this, there should be a warning. Plenty of people won't notice. I've been offered the choice of returned the delivered item and then re-ordering or accepting a gift voucher as a 'goodwill gesture'. I've had to accept the voucher as I simply don't have time for the other option. To use it I'd have to give them more money as nothing on the website costs as little as the voucher is for.