I had something similar happen when ordering a Straight Talk phone for my son from their website. The site kept giving me error messages that the order didn't go through and I ended up ordering the same phone three times.
After calling, they canceled two of the orders for me and I was happy. It never occured to me to ask to be compensated in any way. Maybe I should have demanded a free phone for my trouble.
If this would have happened sending my mom a gift card, I would have just called her and told her what happened. She wouldn't have thought a thing of it.
It IS, however, annoying that they canceled the second card after they were clearly told not to. I think they were not sure exactly what you DID want them to do about it. The communication both ways could have been much more clear.