Welcome to Justanswer.com, my name is Dustin.I'm sorry to hear about the issue you are having, I will do my best to help you resolve it.
This wont be an easy or straightforward process unfortunately.. Also, you may want to confer with law enforcement because they may want or need access or to subpoena the IP records for that email account with yahoo before you try to have it shut down.
But what you would do to report the account to yahoo would be to email yahoo here *****@******.***
Explain to them briefly, the situation and tell them you are reporting that account for fraud and abuse against your name and identity.
It may take some back and forth between you and the yahoo team before you will be able to get the account closed. If you have any further questions, let me know.
Dustin S.Senior Technician and Network Switching Systems Operator / Maintainer.
There is a way.. Through law enforcement and a court order.. Otherwise, yahoo isnt going to give anyone any information..
Here is a contact form for yahoo, you definitely need to start by getting in touch with someone at yahoo support directly and explaining the issue. Definitely explain that material loss, fraud and law enforcement are involved.
I dont work for yahoo.. With that being said, it isnt just Yahoo that turns a blind uncaring eye towards their email users.
Google, hotmail, all the major and free email services do not waste any of their time or resources providing any type of real live help. Neither does facebook, or any other major free online service I know of. You would think that billion dollar companies could afford to provide some sort of live support.
But they do not. Honestly, it will be an uphill battle with your ankles tied together to get yahoo to help you in this situation. Without some sort of court order or injunction.