I signed up for minecraft a long time ago. Yesterday I decided to buy the game so I made a mojang account. My email was already taken (odd) so I used a different one. The username that I always use was also taken so I just used a different one. I downloaded the game and when I try to play it is says User Not Premium. I was wondering if I messed up somewhere in the migration or something.. (Also, I used paypal)
Try waiting for a couple of more hours to see if it was a late activation or not. You will know if you are migrated or not if you are using your email as your username. If it still does not update, try contacting Customer Support under Account Problem: http://help.mojang.com/customer/portal/emails/new
Mojang - Minecraft help