Just for your convenience, I’ll copy here the latest Azure AD announcement about the reirement of the old admin portal:
Use the new Azure portal to manage Azure Active Directory
By January 8, 2018, you should plan to rely fully on the new administration experience for portal-based administration of Azure Active Directory.
The Azure AD experience in the classic Azure portal, and the Azure classic portal itself (https://manage.windowsazure.com), will be retired on January 8, 2018. You are receiving this email because you or another user in your organization recently used that experience.
Here are some resources to help you transition to using our new admin experience:
To give feedback, submit a feature request, or vote on existing feature requests from others, go to the admin portal section of our Feedback Forum.