There are browser security restrictions that prevent messages and events from being passed between the parent frame and an IFrame, especially when the IFrame loads a page that is not in the same domain as the current web page. This is to prevent all sorts of malicious attacks that I won't get into here.
The only way you can know what is happening in an IFrame that loads a third-party page is if that third-party page posts "messages" back to the parent frame via the postMessage() browser API. But to do so, you need to be able to add code to that third-party page. In your situation, you don't have control of that third-party page, so you're basically out of luck.