My Gmail Account Hacked: Supercell ID Stolen and Used by Someone Else

My Gmail account has been hacked. Although I can still access my Gmail and have changed my password, my Clash of Clans Supercell ID has been stolen and is currently being used by someone else, possibly from Russia. I am unable to get support within the game and email support has not been effective.

I have been playing for nearly 10 years, and this is the first time such an issue has occurred. I would greatly appreciate any assistance in recovering my Supercell ID and securing my account.