If you cannot connect to your account, you can still download the license key for your specific version of Sitefinity and place it in App_Data/Sitefinity.
You need to navigate to your downloads and select the proper version for your license. I have outlined the steps in the attached screenshots.
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items