Default Air gesture problem

Hello,

I have seen a lot of themes, but non of them can help me ... all the sub options are on but non of them work. Air gesture is not working at all .. when I am making a phone call the screen turns off imediatelly, like there is something on the sensor ... when I called Samsung they told me it was a software problem. Factory reset did not help... my device Is gt-i9505 running on stock 4.3. Any ideas? Ty for your help ...