child index.php does not overwrite parent index.php in twenty fourteen theme

The way you enqueueing your stylesheets are wrong. Someone very ignorant keeps changing my edit in the codex. The way you are doing this loads your child stylesheet twice. I have already done a post on this that you should check out here

The correct way is

add_action( 'wp_enqueue_scripts', 'theme_enqueue_styles' );
function theme_enqueue_styles() {

    wp_enqueue_style( 'parent-style', get_template_directory_uri() . '/style.css' );

}

As for the problem with your index.php, you should clear all your caches, browser and plugin caches. This really seems like a cache problem as your code looks fine