I bought minecraft today and created a microsoft account. Then I was on this X-box thing and should write a name?

But no matter what I wrote I couldn't create the account (it was probably already taken) So I deleted the name and created my account without a name. Suddenly my name is Scherefarn84749? When I went to the x_box page to change the game day it was just gray, I can't change my name… I logged out of my account, reloaded the page. Nothing. I'm really desperate, thank you in advance for the answer.

You may need to confirm your email. If it still doesn't, you probably accidentally changed your gamertag again because of the fast trading. I would recommend you to contact the support. The support is there for you 24/7.