An answer to what? You can either prove you own the account, or you can't.
https://bitcointalksearch.org/topic/recovering-hacked-accounts-or-accounts-with-lost-passwords-497545
If you can prove it as outlined above, and you did send a signed message, then read this. https://bitcointalksearch.org/topic/m.7637780
I could not figure out how to prove it to you? .. I will give you my email I wrote you will see if it is, send me an email message, I will return you an answer then you will see that I am. If not, can it be deleted and maximum you add me My forum posts are 42 posts new profile
The thread that BadBear linked you to contains explicit instructions on how to recover a lost account. Following those instructions is the only way that you can regain access to your account. Theymos does not want you to reply from your e-mail address because there is a chance that it had already been compromised as well. A proof of ownership of a Bitcoin address that you -- the "original owner" -- have previously claimed to have singular access to before the account was "hacked" is the only proof that Theymos needs.
To further simplify things, consider this example. Let's say that you sent Theymos a PM containing a Bitcoin address that you have ownership of a long time ago. For the sake of simplicity, let's say that the Bitcoin address was 1AccountIsMine1234. If you can link back to that PM, then you can prove that you, the "original owner," owns that address. Having proved that you owned 1AccountIsMine1234, you can then digitally sign a message using that address, thereby proving that you also own the account.
E-mail replies and Bitcoin addresses that have not been previously claimed by you are not valid because there is no way to prove or disprove that you are the original owner from only those. It's a chicken-and-egg kind of thing -- you either need the chicken or the egg first. In your case, you have neither.