"Username has already been taken" when it has not been

Just bought Java and would like to play it, but I get the message of my username already being taken when it shouldn't be. I can play bedrock just fine, but I bought the bundle for java edition.

Furthermore, I can't make the username via the website as the button when I click it goes grey (As in the picture) and then nothing happens. I have tried uninstalling the launcher twice and that hasn't solved the issue either.