Step 1: Open BlueStacks while your PC/Laptop is not connected to the internet.
Step 2: Go to Settings/Apps
Step 3: Select Running Apps
Step 4: Stop all unwanted services such as Game-pop Home, AppCaster, Google services, especially Google Store, or any other such unwanted service.
Voila.! Now you can start your internet connection.
P.S. :- You have to repeat these steps every time you start BlueStacks. It'll take just a minute or so. And still if you get a notification of any unwanted game or application that starts downloading, you can follow the following steps:-
1.Go to Settings/Apps/All.
2.Search for the culprit (such as AppCaster, GamePop,etc)
3.Select "Force Stop".