The primary portal for managing support requests is the Microsoft 365 Admin Center at https://admin.microsoft.com. However, this creates a logical deadlock in your specific scenario: accessing this portal requires valid credentials for the tenant in question, which you have stated is inactive and inaccessible. If you cannot log in to that URL, you cannot generate a ticket digitally.
In this situation, the "portal" you actually need is the directory of Global Customer Service phone numbers, located at https://support.microsoft.com/en-us/topic/customer-service-phone-numbers-c0389ade-5640-e588-8b0e-28de8afeb3f2
The action plan for you is:
- Find your region: Scroll down to your specific country/region in the list.
- Call the number: Dial the number provided.
- Navigate the IVR: You will likely hit an automated system. Do not select options for "Home" or "Personal" use. Select options for "Business" or "Commercial" support.
- Keyword: If asked for the reason for your call, say "Data Protection" or "locked out of tenant".
- The Request: Once you reach a human agent, clearly state: "I need to open a Data Protection case. We have a device locked by Autopilot to an inactive tenant where the admin is gone, and we have the proof of purchase."
I hope you've found something useful here. If it helps you get more insight into the issue, it's appreciated to accept the answer. Should you have more questions, feel free to leave a message.
VP