Someone changed the password of my Google account. I tried to recover it by using Google recovery, but unfortunately that someone has already changed the phone number and the other email address that is needed for the recovery of my account. So I tried other options like answering the questions that Google gave me. One of the questions there is "when did you create your account". I really can't remember it and I'm so frustrated. I hope someone can help me to recover my account.
My friend had a similar issue. You need to contact Gmail support regarding this issue.
You need to prove Google that this is your account. You can do that by mentioning your previous phone number, email, address, a few of contacts which are in your account, a list of most contacted addresses, etc. The requirements which I am telling now was used couple of months back, but the terms could have been changed.
You could find more information and you can use this Google support page to contact Google.