Resizing featured images?

So, I’ve added some featured image dimensions to my theme, but for some reason those are not used as I thought.

from functions.php:

<?php add_theme_support( 'post-thumbnails' );
if ( function_exists( 'add_image_size' ) ) {
	add_image_size( 'archive-thumb', 150, 100, true );
	add_image_size( 'single-thumb', 300, 200, true );
}
?>

from single.php:

if ( has_post_thumbnail() ) { // check if the post has a Post Thumbnail assigned to it.
	the_post_thumbnail('single-thumb'); }

If you take a look over here:

https://www.vezbe.org/wp/test-post-7/

this is how it looks:

‘<img width=”300″ height=”200″ src=”https://www.vezbe.org/wp/wp-content/uploads/2014/05/pixabay/3/dinner_1400717547.jpg&#8221; class=”attachment-single-thumb wp-post-image” alt=”Breakfast, Dinner, Egg”>’

My question is: why is it using a full image, when there is a smaller size available:

https://www.vezbe.org/wp/wp-content/uploads/2014/05/pixabay/3/dinner_1400717547-300×199.jpg

Thank you!