Motorola Defy :: Dust Entering Behind Screen Mainly At Top Left Corner

I brought my Defy in October 2011. Since then it was four times at service. Dust keep entering behind the screen, mainly at the top left corner. Two times they cleaned it and replaced some rubber parts there. Nothing changed, after one or two weeks the dust appeared again. I asked them to send me a new one, but they refused it. A month ago they send me back the same phone without even cleaning it with notes that I'm using it in highly dusted environment against the IP67 (which is theoretically impossible in my country) Now, the whole upper part of the screen is dusted (see photo) and the screws are damaged due to the continuous repairs.