Admob interstitial ads - Deleted a jar file

Hi guys, I followed the official github's instructions to -see below-

Add the google-play-services_lib folder, located at ANDROID_SDK_LOCATION/extras/google/google_play_services/libproject, into the Plugins/Android folder of your project.

But by doing so, I am getting the error of converting java classes to dex classes due to multiple instances of jar files. (researched a lot and many are telling me to check for multiple jar files in the project) And I did.

I realised it's because the google-play-services_lib folder contains similar unity-plugin-library jar files in the GoogleMobileAdsPlugin folder that is installed when I imported the whole unitypackage file. I deleted the copy in the google-play-services_lib folder and I am able to compile the app finally.

However when I tried to run my game on my phone, ads are NOT showing! Not sure why also, but I don't think it's because of my script. Below is my script in case I am wrong.

 using UnityEngine;
 using System.Collections;
 using GoogleMobileAds.Api;
 using GoogleMobileAds;
 
 public class restartGame : MonoBehaviour
 {
     // Use this for initialization
     
     public InterstitialAd interstitial;
 
     void Start()
     {
         RequestInterstitial();
     }
 
     private void RequestInterstitial()
     {
         #if UNITY_ANDROID
         string adUnitId = "ca-app-pub-myadsunit";
         #elif UNITY_IPHONE
         string adUnitId = "ca-app-pub-myadsunit";
         #else
         string adUnitId = "unexpected_platform";
         #endif
         
         // Initialize an InterstitialAd.
         interstitial = new InterstitialAd(adUnitId);
         // Create an empty ad request.
         AdRequest request = new AdRequest.Builder().Build();
         // Load the interstitial with the request.
 
         // Load an interstitial ad.
         interstitial.LoadAd(request);
     }
 
     private void ShowInterstitial()
     {
         if (interstitial.IsLoaded())
         {
             interstitial.Show();
 
         } else    
         {
             Debug.Log ("Interstitial is not ready yet.");
         }    
     }
 
     public void resetScore()
     {
         ShowInterstitial();
         Application.LoadLevel(Application.loadedLevel);
         lightningKills.i = 0;
         cuteCube.isDead = false;
     }
 }