Displaying a specific category in a WP loop - php

Question

On my WordPress website, I created a page in which I display 9 posts of the category "interviews". Then there is a button ("Charger plus d'interviews") to click if you want to see more posts of the category.
There is a problem in the loop, because when I click on it, it displays posts from all the other categories.
What shall I do to display only the "interviews" ?
<section class="blocs" id="home_article_derniers">
<div class="iso-container">
<?php
$post_home_query = new WP_Query(array(
'post_type' => 'post',
'category_name' => 'interview',
'posts_per_page' => 9,
'orderby' => 'date',
'order' => 'DESC',
'post_status' => 'publish',
'paged' => 2
));
if($post_home_query->have_posts()){
while ( $post_home_query->have_posts() ) {
$post_home_query->the_post();
get_template_part('loop-post', 'actus');
}
wp_reset_postdata();
} ?>
</div>
</section>
<div class="separator">
<a class="btn btn-default more-article" data-paged="1" data-post-not-in="<?php echo implode(',', $array_post_not_in) ?>">Charger plus d'interviews »</a>
?>
</div>
This is the code of the loop :
<?php $color = wami_get_first_category_color(get_the_ID()); ?>
<article data-id="<?php the_ID(); ?>" class="post post-actu iso-item bloc-infinity <?php echo (isset($phone) ? $phone : '' ) ?> ">
<a href="<?php the_permalink(); ?>">
<div class="post-header">
<?php
if(has_post_thumbnail()):
the_post_thumbnail('actu-hp-small');
endif;
?>
<div class="overlay">
<div class="img"></div>
<div class="background" style="background-color:<?php echo $color; ?>">
</div>
</div>
<div class="post-header-title">
<?php wami_the_first_category(get_the_ID(), false, $color, true); ?>
</div>
</div>
<div class="post-body">
<?php
the_title( '<h2>', '</h2>' );
/*the_excerpt();*/
?>
</div>
</a>
</article>
Here's the function
function wami_load_more_posts(){
if ( isset($_REQUEST) ) {
$paged = $_REQUEST['paged'];
$post_not_in = explode(',', $_REQUEST['post_not_in']);
$args = array(
'post_type' => 'post',
'posts_per_page' => 9,
'orderby' => 'date',
'order' => 'DESC',
'post__not_in' => $post_not_in,
'post_status' => 'publish',
'paged' => $paged
);
if(isset($_REQUEST['category_in'])){
$args['category__in'] = $_REQUEST['category_in'];
}
$homeblog_query = new WP_Query($args);
if( $homeblog_query->have_posts() ):
while($homeblog_query->have_posts()):
$homeblog_query->the_post();
get_template_part('loop-post', 'actus');
endwhile;
endif;
wp_reset_postdata();
}
die();
}
add_action('wp_ajax_wami_load_more_posts', 'wami_load_more_posts');
add_action('wp_ajax_nopriv_wami_load_more_posts', 'wami_load_more_posts');