How to remove popup ads (Example: Congratulations ads) on Android and iPhone.
When you see a pop up like this, don’t use the “close” button to close the window. Instead, close your entire browser or application that is running.
Clear your browser history (Safari / Chrome) on your device. Click here for instructions on how to do this.
** The facebook app uses its own web browser. If you continue to see popup ads, you may need to clear your browsing history in the facebook app as well or possibly uninstall the app completely.
WARNING: If you end up uninstalling the app and installing a clean copy, you will more than likely lose any data associated with the app and your account.
Open the Facebook app
Click on "settings & privacy"
Click on "settings"
Click on "media and contacts" then scroll to "Clear your phone's browsing data"