So I'm back after a month. But my phone is still at the service. I don't know what happened to my phone, maybe it's lost somewhere. Because I still haven't got any any answer from the service. Nevermind. I found a photo of Lumia 928-925 (I don't know which one) that has exactly same problem as mine. I found it on wpcentral news and you can check there if you still don't believe me (thread about note+) Look at the bottom of screen. You'll see dark area. It's clearly seen on blank internet explorer page or on the white background.