LibGDX Android Gdx.app.exit() doesnt work, how to close app in another way?

I’m trying to close template app for android (5 sec after render() method is started).
Application is closing, but activity is alive in backgroung and I can back to app if I want.
When I’m using this.dispose() without timer, right in the end of render() method it works fine – no activity to resume Application, but when gdx draw anything this issue occures.
I’ve tried put in timer: Gdx.app.exit() / this.dispose() / System.exit(-1) and nothing helps if render() method already working some time.

Here is the code:

public class MyGdxGame extends ApplicationAdapter {
SpriteBatch batch;
Texture img;
MyGdxGame instance;
boolean isReadyToClose = false;

@Override
public void create () {
    instance = this;
    batch = new SpriteBatch();
    img = new Texture("badlogic.jpg");
}

@Override
public void render () {

    Gdx.gl.glClearColor(1, 0, 0, 1);
    Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
    batch.begin();
    batch.draw(img, 0, 0);
    batch.end();

    if (!isReadyToClose) {

        isReadyToClose = true;

        new Timer().scheduleTask(new Timer.Task() {
            @Override
            public void run() {

                //instance.dispose();
                Gdx.app.exit();

            }
        }, 5);

    }

}

@Override
public void dispose () {
    batch.dispose();
    img.dispose();

    System.exit(-1);
}
}