To answer your question -
Yahoo/Att takes account of privacy and security very seriously and will return the account back only when you provide enough accurate information to prove that you are the rightful owner. To recover your account please go to the Account Recovery Form. Take some time with this form and give your best to provide the most accurate answers. That's the only way to prove that you are a rightful owner.
It is extremely important that you keep your recovery options up to date since that is your only way back in if you don't have the password.
There are 2 ways to recover your yahoo account
First , fill out this form please click here: https://help.yahoo.com/kb/account enter as many details as possible to prove that you are the true owner of the Yahoo account. Yahoo will verify your account and contact you in 3-5 business days. They will respond to you via email and sent you a link to reset your Yahoo password.
Second, is to contact Yahoo/ATT through phone support in the United States at(###) ###-####
We best recommend a conversation through the phone because they going to ask you some sensitive information that can only be given over the phone and in addition, they need to validate your information.
Thank you very much for your time & patience while I typed up your response. Let me know if you have any follow up questions. I am here to help you.