So I ordered from Apple.com on September 24th using 3 Apple gift cards (that I had added to my Apple Wallet). On the 26th, the order was canceled and within the next day only one $100 Apple gift card showed back up in my Apple Wallet. The other 2 gift cards (a $50 card and $32 gift card) still showed $0 balance. I called Apple support and they said I should see the balances return to those 2 gift cards on October 5th. The balances never showed up on the 5th. I was just about to call Apple again, and checked the gift cards in my Apple Wallet, and on October 12th, I finally received the balances back on the gift cards. So essentially, it may take over 2 weeks to see the balances to return on your gift cards after cancelling an Apple.com order.