error in account migration process

I purchased Minecraft in November 2011, but now I can't use it.

The site says that my old Mojang account has been migrated, but it clearly hasn't, as I can't use my Minecraft license with my current account

when trying to migrate at:

https://account.mojang.com/migrate

it says:

Error! Your Minecraft account has already been migrated to a Mojang account.