Connect your device, Open your Designer, scroll to the bottom of the "Properties Window" and you will see:
Click these while observing your devices screen.
Navigation Bar Visible will switch on and off the "Title" at the top and
Navigation Toolbar Visible will do the same for the white bar at the bottom.
Now, if you go back to your code after switching these off and the problem persists, then you are most likely activating them in the code as the page loads with
Nav.NavigationBarVisible = True
Hope this helps a bit !!