nickname change

Hey, i made 2 account where I bought minecraft. I was using one nickname on my first account but i wanted it on my second account because I want it as a main account. I could not change name on second account because it already existed so I changed nick on my first account so I can give it to my second acc. After more than month it still shows that this nickname already exists but I don't think anyone name themselvs like me. Can you help me resolve this problem please?