Android Phone - No Fullscreen | no black bars displayed

We tried to play our game on an Android Phone, the game is fullscreen but there is a small border at left and right with a screening error. Does someone has a idea how we can solve that and get the screen without border. We had this problem just on Android phone such as NEXUS 5 and LG G3
Added a Screenshot

which resolution does the game have and what resoludtion do the phones have ?

The game has 320 x 200
The phone has 1920x1080

On Windows and Mac it scales right. So with that resolution there are borders, thats okay. But they should be black...