Can't call up adobe support portal to get serial number for Photohop CS6

Hello,

last year I bought Photoshop CS6 Extended Student&Teacher via Amazon. I downloaded and install Photoshop on my Mac and use the Testtime.

Now I want to get my serial number and Amazon gave me a "Step by Step Plan". In this plan is this Weblink: https://www.adobe.com/de/account.sign-in.supportportal.html .

On this website I could ask my serial number, but when I open this link it is loading and then they stand "413 Header length too large" and next to the weblink is "JRun Servlet Error".

I have also tried other links but then came out the same.

Have anyone a solution for me, please?