I've had a Mojang account since I bought Minecraft years ago.  The launcher told me I needed to migrate my account to a Microsoft account.  I did so.  I just tried to log on using my Microsoft account, and the launcher IS TELLING ME I NEED TO RE-BUY THE GAME !!!!!!!!

Fix this NOW.  I will continue to login using my Mojang account for the time being.  This stupidity should NEVER happen when migrating accounts, EVER.