cant change skin

When i go to change my skin it says "You have to purchase the game to change skin."I got the game at "https://minecraft.net/store/minecraft"
around when 1.3. came out.I paid about 25 american dollars ,i dont really remember how much money i exactly paid though. I seen the same problem on the internet. It seems some other people have the same problem also. I was hoping you cuold find the problem and fix it please. thank you