Google India — Gmail account hijacked but no response from google

On 19 aug 2015, my gmail id vikash.[protected]@gmail.com was hijacked and all security details has also been changed and double verification is also activated from other mobile number. I am trying to recover that account and also mailed google help support but not getting appropriate answer from them. That account is very very important for me and i can also submit all my identity document to prove that i am the real owner of that account. Please help me getting back my account.