Changing the name on my battle.net account

Pretty much at the time i made my account a few years ago i didn't put my actual last name in and forgot about it.

And it won't let me change from battle.net options, from what ive heard from people i'd need to call in and provide proof of a legal name change to get the name on my account changed...but i think its pretty obvious my last name isn't a bunch of question marks so i want to know what i should i know/have when i call about this..