Gmail — gmail account recovery

My gmail account is [protected]@gmail.com.15 day's back this account is disabled. I don't know why it is disabled. Now i am trying to enable this account and following all the procedures of account recovery process.

Problem is alternate email id for verification code is not used by me so many years that is why i don't know the password of this email id.
Because of this reason they are assuming that i am not owner of this gmail account

Please help me i am very frustrating
This account i am using from last 8-9 years is very important for me.