I don't work for Kobo either and I also think expecting them to just give you a $50 dollar gift card is plainly ridiculous. Also, I have a mother and if something like this happened to me I would have just called her and explained that the website glitched and she was only supposed to receive one gift card. My mom is a nice, reasonable lady, and I know she would understand. I just don't see the big deal.
But then again if the attitude and personality you're showing here have anything to do with how you were raised I'm guessing your mom isn't as nice and reasonable as mine is.