iOS developer program terminated for unknown reason

We recently submitted a social networking iOS app and it is in "Waiting For Review" status. It has been rejected for a couple times due to different reasons but all these issues have been addressed and fixed so we are hoping this latest submission will get approved.

But two days ago we suddenly got a letter from apple saying our iDP Agreement is terminated due to "distribution your Application in an unauthorized manner outside of the App Store". We are totally shocked and have no idea what happened. Our app hasn't been approved and released in App Store and we don't even know where else we can submit and distribute this app. Is it Apple made a mistake (I called Apple Developer customer service, they said they would ask around but don't have answer either)? Or is it possible our code got stolen or hacked by someone and put somewhere we don't even know?!

We would greatly appreciate if anyone can provide advice! Especially, what that "unauthorized distribution" could be? What would be a purpose of unauthorized distribution of an unpublished iOS app?

Thanks!