This is how to fix WhatsApp application not installed on MTK phones that has the package name conflicts…. And any other pre-installed apps
You need root access on your phone…
1. Uninstall the official WhatsApp.
2. Install Root Browser and Launch it. (it will ask for you to grant it superuser permissions. So grant it)
3. Navigate to system > vendor > operator > app.
4. In the last folder after navigating tosystem\vendor\operator\app you’ll find a list of apps there. Now delete the WhatsApp apk file with the green icon in there.
5. Now restart your device