Username

I'm having some issues with my username not being 'valid.' When I enter my username on voting sites for servers and server stores it states that my username isn't valid. This is not the case however as I'm playing mine craft with that username and have been for years now. My user name is Chxxical and I've typed in my user on these sites with the correct uppercase and lowercase letters. I've also tried putting my username on other server sites and voting sites and it states the same thing so the issue isn't working aspiria. I just want to be able to support servers and I can't do that is the issue with my user is still playing

up.