How to implement AdMob after iAd fails mediation - ios

Question

I implemented for iAds to works in bannerViewDidLoadAd method and then I implemented for AdMob to work in didFailToReceiveAdWithError method. However, on the same view controller I have a GameOver method where I want ad to appear. Only iAds load on GameOver method, AdMob doesn't. Also, when iAds fail to load AdMob doesn't load. It seems to me since I added the GADBannerView programmatically onto Storyboards the game never responds to _bannerView.hidden=YES or NO. Since i Added the ADBannerView from Object Library in Xcode, the game only responds to iAdBanner.hidden=YES or NO. Why doesn't AdMob respond to a programmatically added Ad banner?
-(void)bannerViewDidLoadAd:(ADBannerView *)banner{
[UIView beginAnimations:nil context:nil];
[UIView setAnimationDuration:0];
[iAdBanner setAlpha:1];
iAdBanner.hidden=NO;
[UIView commitAnimations];
[self.iAdBanner setDelegate:self];
_bannerView = [[GADBannerView alloc] initWithAdSize:kGADAdSizeSmartBannerPortrait];
}
-(void)bannerView:(ADBannerView *)banner didFailToReceiveAdWithError:(NSError *)error{
[UIView beginAnimations:nil context:nil];
[UIView setAnimationDuration:0];
[iAdBanner setAlpha:0];
iAdBanner.hidden=YES;
[UIView commitAnimations];
_bannerView = [[GADBannerView alloc] initWithAdSize:kGADAdSizeSmartBannerPortrait];
_bannerView=[[GADBannerView alloc]initWithFrame:CGRectMake(0, 0, 320, 50)];
self.bannerView.adUnitID=#"UNIT-ID";
self.bannerView.rootViewController=self;
[self.view addSubview:self.bannerView];
self.bannerView.delegate = self;
GADRequest *request =[GADRequest request];
request.testDevices= #[ GAD_SIMULATOR_ID ];
[self.bannerView loadRequest:request];
}