I'm trying to import my old Premium Minecraft Account to my new Mojang account?

When i log into the Mojang accound and select to migrate it it asks for my Username and Password BUT when i put them in it says that the username and or password are wrong but i know they are right as i have recently changed them…
I tryed to log into minecraft website and do passsowrd recovery incase but it said that my user name doesn't even exsit. I know it does coz i can log into minecraft game with it and it shows when i log in too… WHAT DO I DO!