MY Account got hacked.. Need Help.help

So, last year my gmail account was hacked by a Russian hacker. He replaced my gmail address with his own and then sold the account to someone else. The buyer then updated the email to their own. Fortunately, I was able to recover my gmail account, but since the email linked to the game was changed by the buyer, I’m unable to update it back to my own gmail. My game account is still logged into my mobile phone, so I have access to it, but I’ve contacted support with my game account and they haven’t been able to help so far. Please help me.