Composer, php-diff and Class Not Found problems

Hoping someone can point out the error of my ways. Haven't used composer very much, but it appears to have properly loaded the files, but I am still getting the dreaded "Class "DiffHelper" not found" error.
1) Installed the library with composer: "composer require jfcherng/php-diff"
2) Verified the files are there (/_site/vendor/jfcherng/php-diff/src/DiffHelper.php)
3) Added to the top of my controller: "use Jfcherng\Diff\DiffHelper;" (also tried "use DiffHelper;")
4) In my view file called: 

PHP Code:

<?php
 $changes = DiffHelper::calculate($oldRecord[0]['comments'], $oldRecord[count($oldRecord)-1]['comments'], 'Unified');
 echo $changes;
 ?>

Ran the page and got the "Class not found" error! Feeling like I missed a step somewhere.

Thanks in advance!