I have decaped more than 25 people in a day it says on the achievement in a week I completed it in one day I have saved all the replays where I decap the peoples heads and decaped them.
And I have not been given the ahievement it just goes back to 25 and I decapped the people in abd and erthtk but still nothin received.

Also I have 3rd Dan black belt and I was about to upgrade and I got to 3 games to 4th Dan and it I won a game and it still said 3 games till 4th , I changed servers to see if that will work but still not.