I have an existing CS6 membership for PC and would like to take advantage of the $29.99 offer for the complete CC. I would like to keep my CS6 for PC and would like to use the CC on my Mac. I also have a recurring monthly photographer CC. My problem is when I attempt to upgrade the only options that are available are for the $49.99 monthly fee.
You should check the terms for the special you wish to take advantage of as it might only apply to a specific class of customers. That might explain why you do not have the option.
If you wish to change your subscription in some way then you will have to contact Adobe Support thru chat or by phone when they are available.
For the link below click the Still Need Help? option in the blue area at the bottom and choose the chat or phone option...
Make sure you are logged in to the Adobe site, have cookies enabled, clear your cookie cache. If it fails to connect try using a different browser.
Creative Cloud support (all Creative Cloud customer service issues)
http://helpx.adobe.com/x-productkb/global/service-ccm.html ( http://adobe.ly/19llvMN )