This happened to me a couple of years ago. Lost my phone, no recovery codes, so no access to github. Contacted support, they told me that they wouldn't be able to restore access even when I was communicating with the email associated with my account.

Luckily I only had public repos, so I created a new account and forked them all. Support had told me that if there isn't any login activity in the blocked account for a period of six months, they would delete the account and release the username. And yes, I had to follow up after six months were up to make that happen.