Gift Card Scam

I purchased a gift card for "all things apple" The card was sold to me by a major retailer. I got home and the receipt says it was activated. I tried to load the card, it says the code is invalid. I called Apple and was told to file a police report b/c it was a matter of theft. Went back to the retailer, filed a claim and it was twice denied. Apple says the card was cancelled one hour after purchase. Retailer will not refund my money and charging interest on my credit card balance. Apple won't honor the card. What else can I do? I want my $100 back!