Cancelled order arrived anyway. Can I keep it?

[R. Trout]

I misordered computer software and called three hours later to cancel it and they said yes, it was cancelled and they removed the charge from my credit card. I really wanted it but had to settle for a cheaper version of it. Four days later, they mail the software anyway. I called my credit card company and they said they did remove the charge days ago. I want to keep it, but because it's worth $800 I feel kinda guilty about it, but then again it's nowhere near the large amount of money I've spent on their software in the past!