$new_post = array(
'post_title' => $title,
'post_content' => $content,
'post_status' => 'pending',
'post_date' => date('Y-m-d H:i:s'),
'post_author' => $user_ID,
'post_type' => 'post',
'post_thumbnail' => $file,
'post_category' => array(28,1)
);
$post_id = wp_insert_post($new_post);


$attachment = array(
'post_mime_type' => $wp_filetype['type'],
'post_title' => preg_replace('/\.[^.]+$/', '', basename($filename)),
'post_content' => '',
'post_status' => 'inherit'
);

wp_insert_attachment($attachment);


$wp_filetype = wp_check_filetype(basename($filename), null );
$attachment = array(
'post_mime_type' => $wp_filetype['type'],
'post_title' => preg_replace('/\.[^.]+$/', '', basename($filename)),
'post_content' => '',
'post_status' => 'inherit'
);

$attach_id = wp_insert_attachment( $attachment, $filename, $post_id );
require_once(ABSPATH . "wp-admin" . '/includes/image.php');
$attach_data = wp_generate_attachment_metadata( $attach_id, $filename );
wp_update_attachment_metadata( $attach_id,  $attach_data );

add_post_meta($post_id, '_thumbnail_id', $attach_id, true);