My friend cant login into his account since the username change

My friend owns two accounts, both gold. He has permanently lost one apparently He told me he can no longer log into it since the username change, I told (like an idiot) 'just change the username its mandatory', but he cant change it since he cannot access his account. He sent an email/ticket to support through his other account and apparently they cant confirm ownership despite him sending all of the information. Any clue how he can solve the issue?
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