Yahoo mail has suddenly disappeared from my iPhone 5 inbox

I've had Yahoo email on my AT&t iPhone 5 for a year. Yesterday, with no action on my part, and no changes to the settings on my iPhone, all my Yahoo emails disappeared from my iPhone inbox, and no new emails sent to my Yahoo email address are appearing there. The Gmail inbox on my phone is fine. I can access my Yahoo mail on a browser, but not on in my iPhone inbox. I have reset network settings, deleted my Yahoo mail account, re-booted the iPhone, and re-added the Yahoo account. Nothing helps. I have no idea if the problem resides with Apple, Yahoo, or AT&T. Has anyone had the same problem? What can I do?