Gmail — recover my account

Dear team,
My account [protected]@gmail.com is in hands of an unknown person. I linked my account with the game clash of clans and to play that game my friend gavee the details of my account to unknown one. They changed the baseline data such as my password, phone number and recovery email. Now i'm unable to sing in my account, but i need that account for many purposes. I tried to recover it but google coun't verify my account. Kindly look into this issue and help me to recover my account
Yours faithfully
Akhil attingalkaran