I see in your post history that you have posted some addresses back in 2016.
Can you sign a message from an address you have posted here in the past?
It's a way to get your account at least tagged and probably useless for the scammer, he may also be willing to give it back if it's not worth it anymore.
Best proof I can provide (based on public posts and not private messages) is this.
1. Back in the early days of Ethereum we were playing around with simple smart contracts, building pyramids and lotteries for each other, playing around with various rules and mechanisms etc.
2. Back then I have created this post:
https://bitcointalk.org/index.php?topic=1436754.msg14637462#msg146374623. As you can see, there is this smart contract mentioned in this post:
http://etherscan.io/address/0xa864694cACDf27900aFB3c32b1B07Aea3C465dDe#internaltx4. As you can see in the block explorer, the creator of this smart contract is this address:
https://etherscan.io/address/0x97eedb324b5ab7ddd100d027e990a05037e61b375. And yes, I still have the keys in one of my backups and can use them to do whatever is necessary to prevent the person from exploiting the account further.
-----BEGIN ETHEREUM SIGNED MESSAGE-----
My account Qiuyue201 has been hacked/lost. Please reset the email to
ICO_services@gmx.com. The current date is 23 October 2018.
-----BEGIN SIGNATURE-----
0x97EEDB324b5AB7DDD100d027E990A05037E61B37 (addres that has created smart contract 0xa864694cACDf27900aFB3c32b1B07Aea3C465dDe from the linked post)
{
"address": "0x97eedb324b5ab7ddd100d027e990a05037e61b37",
"msg": "My account Qiuyue201 has been hacked/lost. Please reset the email to
ICO_services@gmx.com. The current date is 23 October 2018.",
"sig": "0xd7dbb8c25705936e8bb4d501c20b5155d13a7ea947cc9a03f88310d908a788b203eb13bff9c45
d68347f24e44b183c53da11e887bd9674e3dfcc9988c246696d1c",
"version": "3",
"signer": "MEW"
}
-----END ETHEREUM SIGNED MESSAGE-----
Here is the unedited post where I posted the Ethereum smart contract created by that address:
https://bitcointalk.org/index.php?topic=1436754.msg14637462#msg14637462