Here is the official reply:
Hello,
We understand that you are requesting for a Cross Platform Swap for Illustrator CS5 Mac to Windows and that you incorrectly purchased it from EBAY however, as per Adobe's Policy from Swap and Exchange, we doesn't offer swaps or cross-platform/language exchanges to customers who have purchased a product second-hand or from an auction site such as eBay. We refer the customers back to the point of purchase to arrange an exchange. So what we can advise you it to go back to Ebay and arrange an exchange for the correct software platform that you needed since you just purchased the software last Apri 16,2011.
We do apologized for the inconvinience.
In case you are unable to respond, please be informed that the case will be AutoClosed by our system on the 10th day. However, you don't have to worry because you can always reopen this case within 14 days upon closure through our support portal or by calling our Customer Service anytime at 800-833-6687. We are open 7 days a week 6am-8pm, Pacific Time.
Thank you,
Jean
Adobe Webmail Support