threeonesix on "Pagination issue? Not sure, rookie here"

I shall preface this request by saying that my programming skills are rudimentary at best, I have very little experience with WordPress and that I find myself in the position of maintaining a corporate website built using WordPress without any qualifications for doing so. That being said I believe we are having an issue with pagination and I don't know how to fix it myself. I've spent considerable time reading through dozens of support threads on this site related to the problem so it's not that coming here to ask for assistance was my first thought.

The theme for this website was custom programmed by a contractor with whom my employer no longer desires to have a relationship. Meaning I do not have the ability to reach out to that person for assistance. But I am certain the problem is with his pagination coding, found in the theme's index.php file as follows:

<?php $paged = (get_query_var('paged')) ? get_query_var('paged'):1; $args = array( 'post_type' => 'post', 'posts_per_page' => 10, 'paged' => $paged, 'order' => 'DEC', 'offset' => '0' ); $the_query = new WP_Query($args); if($the_query->have_posts()): while($the_query->have_posts()):$the_query->the_post();?>

The problem is that using the 'Older' and 'Newer' page links on the posts page load only the same 10 posts each time. Is there anything in that code that jumps out as being responsible for this behavior? Is this even the correct code in the index.php file responsible for pagination?

TIA