Something similar to this happened to me the first time I bought a Vanilla Visa Gift Card from OD. I was trying to buy 4 $500 GCs. One of them wouldn't activate properly. Cashier put it aside. Then she activated the other 3 but switched (accidentally) one of the properly activated GCs with the previously discarded one. After a lot of back and forth with Incomm, took about a week and a half for Incomm to activate and fund the GC that I had that was not working.

Lesson learned: always check the tracking number on your receipt with the number located below the bar code on the back of the GC package at the register right after you pay for it. The customers behind you might give you dirty looks, but it's not their money, it's yours.