Originally Posted by Worldwalker
Except the cashier didn't do that. According to what the OP said, she (the OP, that is) conducted the transaction twice -- once believing it didn't work (though not checking it), and once believing it did.
Hold on, something just struck me....
Kobo's email (as quoted by the OP) said that the "purchases happened less than 1 second apart."
The first purchase attempt didn't go through. The "try again later" response was totally accurate, and it wouldn't have appeared in the OP's account because it had, in fact, failed.
If the first attempt didn't go through, then the double-purchase is likely an accidental double-click, and not Kobo's fault (although they still should not have deleted the card sale; they need customer service reps who can tell the difference between "I'm unhappy with this purchase" and "I demand a refund.")
If, however, the first purchase hung in the system and didn't complete until the second one was made, then it's Kobo's fault, and they should eat the cost for the extra card.
I don't speak software; cannot imagine how one would resolve this. Good customer service would involve "oh, hell, just give her the damn card"--because as it stands, she's not likely to buy more cards in the future for other family members, and neither are they. $50 is generally within the range of costs for keeping a cluster of happy customers.