No AD plugins work for me at all - android

as the title suggests, none of the ad plugins work. I have tried almost everything, at least the famous ones..

1 - chartboost

2 - Admob

3 - revmob.

The steps I took:

1 - import the plugin

2 - change the manifest.xml file for android

3 - make it show the ad, (i don't care where I just want it to show for now)

4 - deploy it on device

5 - tested it on emulator (not sure if this is the problem but I doubt it)

help please, this game has been sitting on my computer for a month and i can't figure it out.