When the ad is unresponsive, you can close the game -> re-open it. And your process will not be lost. But please note that just quit the app, DO NOT uninstall it! Here is how to close the game:

Close an app on your iPhone or iPod touch

Find, open & close apps on Android

And you can report those freezing ads by using the "Contact Us" button on the upper right-hand corner of the screen. Send us a screenshot of those ads and we will block them as soon as possible.