AdMob test ads not working on released version of Android app

I have an issue with AdMob in my Android apps. I added my device id as test device id and test ads are working well in my apps inside the debug version but when I create signed release APK and upload it to the Google play and install my app from Google play I noticed that the test ads have been replaced with live ads.There is no test ad label at the top of the ad. So anybody know the reason of this issue and how to fix it? Thanks & Best Regards