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Hi,
Based on your description, you have never migrated your Mojang account to any Microsoft account. According to the Minecraft Article, if you have never migrated your Mojang account to a Microsoft account, it is no longer possible to migrate unmigrated accounts or make the move. Your Mojang account cannot be used anymore, and Microsoft cannot do anything about this since it was never migrated to any Microsoft account.
Information about Mojang Accounts and Microsoft Account Migration
Mojang Account migration completed
Those accounts that have been recovered may have already had their Mojang connected to a Microsoft account.
If you are sure that they never migrated but were able to recover their Minecraft account, I recommend contacting Minecraft for further assistance and clarification. Please go to the link below and fill out the form to request support.
https://help.minecraft.net/hc/en-us/request/new?ticket_form_id=360001225811
If you need more assistance, please let me know.
Stay Safe!