Dismount door panel. VW Polo Net

Sounds like it is a broken window regulator. You will need to remove the door panel to fix it. Mine broke and I can actually pull the window up and it will stay until the vibrations of the freeway eventually make it slide back down again (this would be a temporary fix of course). Anyways, there are a couple screws behind the door handle I believe, and then some snaps around the edges, and some clips along the window line. You should get a Bentley's manual so you know exactly how to fix the window regular.