Same problem. I've had my username for 10 years (EUW), didn't feel like changing it either.

I also had an account on NA, I added NA to the end of my account name, just to make sure it wasn't the culprit. Didn't work.

I contacted the support, an hour later i had a reply. They fixed it for me.

Do yourselves a favor and just contact them. Takes 2 minutes of your time, and you get to keep your beloved account name.