Android : Admob Unity plugin isn't working

I downloaded the Unity admob plugin from https://github.com/googleads/googleads-mobile-plugins. I made a test project and imported the Google ads Unity package, then I inserted my AdUnitID for android into the GoogleMobileAdsDemoScript. I also added the google-play-services_lib under the Plugins/Android folder, and I also added my unice identifier for the android file. Either the banner or the interstitial will work. I have tried many times and made different banners and interstitials. My android sdk is up to date and I'm running Unity Pro version 4.6.3f1(30 day trial). Please HELP me!!