Creative Cloud is not going to link the CS6 version of the software. Try the following page instead:
http://helpx.adobe.com/x-productkb/policy-pricing/cs6-product-downloads.html
You can download the trial version of the software thru the page linked below and then use your current serial number to activate it.
Be sure to follow the steps outlined in the Note: Very Important Instructions section on the download pages at this site or else the download will not work properly.
CS6: http://prodesigntools.com/adobe-cs6-direct-download-links.html
If you continue to have issues with your serial number, you need to contact Adobe Support either by chat or via phone when you have serial number and activation issues.
Here are some links to help make contact:
http://www.adobe.com/support/chat/ivrchat.html
http://www.adobe.com/support/download-install/supportinfo/