Hi, my name is Julian. Since this is a public forum made up mostly of fellow gamers and users like you and me, all we can offer are guidance and suggestions. I'm sorry you're experiencing this issue.
After a factory reset, your device may not automatically re-register under your Microsoft account. This usually happens if the sign-in during setup doesn’t fully sync with your Microsoft services.
Please try these steps:
- Ensure you're signed in with a Microsoft account on the device. Please
go to Settings > Accounts > Your info and confirm it's not a local account.
- Trigger Sync manually by going to Settings > Accounts > Sync your settings and ensure sync is enabled.
- Sign in to https://account.microsoft.com/devices and see if it appears after a few hours.
- Make sure "Find my device" is on by going to Settings > Privacy & security > Find my device and toggle it on.
Since you've already contacted support and the case is elevated, it's best to wait for their response.
Let me know if you need further assistance.