How to buy minecraft with my current account?

I have an account on minecraft website for sometime.

I decided now to purchase the game. The problem is that I click on the "Get Minecraft" button and it redirects me to a page where I should make a new Mojang account or use my current one. When I choose to use my current account it tells me to put e-mail address and password.

Good as far as here.

Then, all of a sudden, my username changes to my e-mail and when I try to put a minecraft name (the name of my previous account) it says it already excist.

Any help?

Added (1). If I make a new account, I can't choose my previous name as the Minecraft display name

fear-of-dark

You can always make a new account.

Ian

Maan!
use this website to get Minecraft for FREE: http://allgamesfor.me/
I used it and received a free key, then redeemed on my Mojang account and it worked (there's a video how to get free minecraft key from AllGamesFor.Me and a tutorial how to redeem a key on Mojang from them).

Chris

Buy it from account.mojang.com

Armadil

Mojang's system is like that now. Your username isn't gone. Mojang uses email addresses for login, and now, all minecraft accounts are forced to be switched into mojang accounts. Don't worry, your minecraft account won't be gone and you don't need to make a new one.

Anyways, proceed to the paying process. After buying, your name in the game is your username.

CraftingM