Plus / Minus Buttons not working

Hi all,

When I click the plus / minus signs to increase or decrease the quantity of an item in the store nothing happens and I cannot figure out why.

I think it may be something to do with the code I have in functions.php but what do you think?

// QUANTITY //
function woocommerce_quantity_input() {
    global $product;
	$defaults = array(
		'input_name'  	=> 'quantity',
		'input_value'  	=> '1',
		'max_value'  	=> apply_filters( 'woocommerce_quantity_input_max', '', $product ),
		'min_value'  	=> apply_filters( 'woocommerce_quantity_input_min', '', $product ),
		'step' 		=> apply_filters( 'woocommerce_quantity_input_step', '1', $product ),
		'style'		=> apply_filters( 'woocommerce_quantity_style', 'float:left; margin: 50px .618em 0 .618em;', $product )
	);
	if ( ! empty( $defaults['min_value'] ) )
		$min = $defaults['min_value'];
	else $min = 1;
	if ( ! empty( $defaults['max_value'] ) )
		$max = $defaults['max_value'];
	else $max = 20;
	if ( ! empty( $defaults['step'] ) )
		$step = $defaults['step'];
	else $step = 1;
	$options = '';
	for ( $count = $min; $count <= $max; $count = $count+$step ) {
		$options .= '<option value="' . $count . '">' . $count . '</option>';
	}
	echo '<div class="quantity_select" style="' . $defaults['style'] . '"><select name="' . esc_attr( $defaults['input_name'] ) . '" title="' . _x( 'Qty', 'Product quantity input tooltip', 'woocommerce' ) . '" class="qty">' . $options . '</select></div>';
}
// QUANTITY //

Here’s a page with the problem.

All help is appreciated!

https://ww.wp.xz.cn/plugins/woocommerce/