i really have no idea what sign message means/how to do that(if there is video tutorial , it would help more) ... why can't they just send "Verify Email" to the first email and that's it? The account had same email for over a year until it got hacked...
Go to here:
https://www.myetherwallet.com/signmsg.htmlThis tutorial might help:
https://medium.com/@eugen_lechner/sign-and-verify-a-wallet-address-with-myetherwallet-1a46f6e2853eGood luck
PS: Try to remember if you ever posted any bitcoin address or any ETH address from your original account. If you did post any bitcoin address or ETH address then try to find it out from that account (do extensive search on your post history page). If you find any then get the access of that address (Bitcoin or ETH) and sing the address.
If that's a bitcoin then do as KWH said and if that's an ETH then follow the above links.
Remember if you never used any ETH or BTC address ever then I doubt you will ever be able to recover your lost account.