查询不会在wordpress中返回结果，但会手动运行

I have the following code in WordPress

$wpdb->show_errors();
$testQuery = $wpdb->prepare("SELECT * FROM $table_name 
                             WHERE service_id = %d 
                             AND   token = %s" , $service_id, $token);
$testResult = $wpdb->get_results($testQuery,ARRAY_A);

echo "<pre>testQuery
$testQuery
";
echo "testResult: "; print_r($testResult);
echo "db error:" . $wpdb->last_error;
echo "</pre>";

When I copy-paste the result printed in my echo to phpmyadmin and run the query, it shows results, however, when running the query within wordpress, my $testResult is an empty array. $wpdb->last_error does not print any error message.

Can anyone point me in the right direction?