Lucy,
The "Contact Support" link on the DE support page will take you to the main support page
at http://www.adobe.com/support/contact/
Once there their is another link called "Ask a new question" which after you sign on with your AdobeID on the right will start up a a new support request.
On this page you will need click on the "Additional products" radio button, and then select "Digital Editions" from the drop down list and then click continue, which will take you to another page so that you can enter in details about your problem
After you are done, click on "Review case & submit".
You will want to return occasionally to the Support portal to review the status of your case.
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-jim