send data via ajax to xml type php

Question

This topic is diffrent from other "ajax to php" topics, im here using xml type php file and I want to send some data to this php file via ajax, but php is not retrieving any data from ajax. when i remove header function it gets data from ajax. here is my jQuery-ajax code;

        var borcu_son = $('#borcu').val();
        var borclu = $('#borclu').val();

        if(borcu_son > 0){
            $.ajax({
                url : 'borc_takip_xml.php',
                data : {'borcu_son':borcu_son,'borclu':borclu},
                type: 'post',
                success: function(){
                    alert('send successfull!');
                },
                error: function(){
                    alert('ajax failed!');
                }
            });
        }

And php file;

<?php 
    header('Content-Type: text/xml;  charset=UTF-8');
    echo '<?xml version="1.0" encoding="UTF-8" ?>';
    echo '<xml>';
?>

<?php ////////////////// BORÇ OLUŞTUĞUNDA BİLGİLERİ AJAXLA AL //////////////////
    if(isset($_POST['borclu']) && isset($_POST['borcu_son'])){
        $borclu = $_POST['borclu'];
        $olusan_borc = $_POST['borcu_son'];

        $borclu_childs = '';

        $borclu_childs .= '<borclu>';
        $borclu_childs .= '<isim>'.$borclu.'</isim>';
        $borclu_childs .= '<tutar>'.$olusan_borc.'</tutar>';
        $borclu_childs .= '</borclu>';

        echo $borclu_childs;
    };

echo '</xml>';
?>