Follow the instructions. If you can't prove the account is yours by the guidelines, you may be out of luck.
There is part of instruction: There are alternative ways of proving ownership, but they take too much time. In other words, they won't do it.
As i say, i can prove ownership by other ways: I can proof ownership by my other email / Telegram, that i've posted in my topic. I can proof my ownership by Skype - username still in my profile. I can proof ownership by original email of that account.
Emails can be hacked, accounts can be sold with an account, none of which is proof.
This has been gone over extensively.