How do I recover my Gmail account if I don’t remember anything?

First, they must still have the email address in their system. Some providers clear out old email addresses after a certain number of years. Google or Yahoo probably won't, but smaller email providers may.

Assuming that the e-mail address is still there, you are missing something else that the provider of the email can use to validate/prove that you were the owner of the account. Otherwise, any person in this world can say, "I am Marbella, give me that account."

That is normally your password and recovery email, which you said you do not have.

Your cell phone number, please. This is where the backup email and cell phone number will be sent a link to reset your password to an account.

You might have secret questions and answers if you configured that in advance. I don't like forcing someone to provide using public info to go around a password, but it works as a password reset at times.

If this is a service you paid for, you may be able to identify yourself through payment records, especially if you used a credit card. The trick to this is that the company may refuse. For instance, if you were trying to get an old Verizon email account, and you're now a Comcast subscriber. why would Verizon give you that service for free?