Email used for hacking

HERE is info on how to report such things.

What would be expecting in the way of action by AT&T?

How is an email account "hacking into your business"? 

It's the email that was used to hack into my business Instagram account.  Of course there is someone behind that email.  I need to know how to report that this particular email address is being used to hack into accounts, or at least mine.  They have changed everything on my account to lock me out and now I have to go through all hoops with Instagram to verify my identity, that I am the rightful owner & have been hacked.

AT&T controls the @sbcglobal emails so they would be able to take action to freeze that email account to look into what they have done as I have all of the notifications from Instagram showing that this email was used to change my account.  Maybe they can direct me to the link to file a report.   

If you look at the lists of posts in this forum you'll see that there's a major issue with the security of Yahoo/AT&T email accounts right now.  It's not a stretch to think that some of those accounts have been compromised and used for exactly the situation you find yourself in. I seriously doubt that Yahoo/AT&T would do anything to the account but I'll be interested to hear what they tell you so please do come back and update this thread.