problems with installation (not shortcode)

Hello,
I am not a php/wordpress expert, so please sorry for the question which looks like an easy task to fix.
I added the following code before the loop of single.php file:
if( function_exists('dot_irecommendthis') ) dot_irecommendthis();

Then, just below the loop inizialization:

$no_likes = '<span class="post-stats-label">' . Likes . '</span><i class="fa fa-heart"></i>
<span>' . dot_irecommendthis() . '</span>';

$no_likes is finally added in the position where I want it should be.
No values are registered.
Could you help me? What is wrong on that?

FYI: I have also tried the original code reported in the plugin homepage:

<?php if( function_exists('dot_irecommendthis') ) dot_irecommendthis(); ?>

but it does not work.
Thank you.