I need help with recovering an account. Don't know where to start

So, here's the story: My buddy irl that actually showed me league wayyyyy back before season 1 even started used to play alot and had a decent amount of skins and what not.. well long story short he forgot his password and tried recovering it.. well once he did that he tried logging onto his email and it had been so long even his email needed verification.. so he tried signing onto his backup email to verify his league email to recover the password... well, that secondary email was hacked and he cant get access to either emails now.. So is there any possible way he can log onto that account again?!?! he still has the same credit card that he used to purchase RP on the account.. theres GOTTA be a way to prove that it was his. HELP RITOOO