Hi Sven,
Thanks for taking the time to reach out! On reviewing your account and purchase history with us, it appears that you did obtain a license for Events Calendar PRO in December 2015, which was refunded per your request shortly thereafter. Unfortunately, we’re not able to provide assistance related to the use of products on expired or refunded licensing. You can get up to date with a new Events Calendar PRO key and the latest version of the plugin by grabbing a new license from our products page:
https://theeventscalendar.com/product/wordpress-events-calendar-pro/
Let me know if you should have any questions as you’re completing your new purchase with us–I’d be glad to help! 🙂 Cheers, and thanks again!