“It looks like someone else might be using your account” Verification Problem

I've been having this problem for about a year now and it hasn't really bothered me until now, as I have found some old stuff that I would like to see but can't because they are connected to this email. I have no way to prove this is mine as the alternate email associated with the account no longer exists. I don't know my recent emails as I haven't used the account in quite some time. It's just super frustrating because I've sent in multiple account recovery requests and they have all been denied. What do I do?