Wie kann ich die Testversion von Pro DC kündigen?

you'll need to do more than just uninstall.  actually, cancel your subscription:

https://helpx.adobe.com/creative-cloud/help/manage-cc-individual-membership.html

if that fails to help, using a browser that allows popups and cookies,  contact adobe support during pst business hours by clicking here and, when available, click 'chat', http://helpx.adobe.com/x-productkb/global/service-ccm.html

Un-install Adobe Acrobat Pro.

To Cancel https://helpx.adobe.com/creative-cloud/help/cancel-membership.html

-or reply #1 in https://forums.adobe.com/thread/2023066 - includes Mon-Fri Chat link

Also, trials are 7 days Adobe has announced that Creative Cloud trials have been reduced from 30 days to 7 days, effective immediately.