Edit: Sorry it's the rear one! I had similar issue sometimes it will just not react. But restart the car then use the "all-windows" switch and readjust it and back to normal.
What happens when you press the button? Any noises? Depends if the line snapped or the window switch is not getting any voltage. Check for errors with VCDS sometimes it can flag something.
Look on my build thread. There is a link to a window repair kit.