How to export data from database to excel and force download it? PHPExcel

I have created a code that fetch data from the database, its working except for the last part which is force download into the browser. I don't know whats the problem. This is my code so far..

    $PHP_Excel->setActiveSheetIndex(0);
    $Row_Count = 0;

    $Query = mysqli_query($Connection->con(),"SELECT 
                                              users.User_ID ,
                                              users.First_Name ,
                                              users.Middle_Name ,
                                              users.Last_Name ,
                                              users.Role ,
                                              users.Status
                                              FROM users 
                                              INNER JOIN sections_students
                                              ON users.User_ID = sections_students.User_ID
                                              INNER JOIN sections
                                              ON sections_students.Section_ID = sections.Section_ID
                                              WHERE users.Department_ID = '" . $_SESSION['Department_ID'] . "'
                                              AND (users.Role = 'Project Leader'
                                              OR users.Role = 'Project Member')
                                              AND sections.Academic_Year = '" . $_SESSION['Academic_Year'] . "'
                                              AND sections.Semester = '" . $_SESSION['Semester'] . "'");

    while ($Row = mysqli_fetch_array($Query)) {
        $PHP_Excel->getActiveSheet()->setCellValue("A" . ((String)($Row_Count)),$Row['User_ID']);
        $PHP_Excel->getActiveSheet()->setCellValue("B" . ((String)($Row_Count)),$Row['First_Name']);
        $PHP_Excel->getActiveSheet()->setCellValue("C" . ((String)($Row_Count)),$Row['Middle_Name']);
        $PHP_Excel->getActiveSheet()->setCellValue("D" . ((String)($Row_Count)),$Row['Last_Name']);
        $PHP_Excel->getActiveSheet()->setCellValue("E" . ((String)($Row_Count)),$Row['Role']);
        $PHP_Excel->getActiveSheet()->setCellValue("F" . ((String)($Row_Count)),$Row['Status']);

        $Row_Count++;
    }

    $PHP_Excel->getProperties()->setCreator($_SESSION['Name']);
    $PHP_Excel->getProperties()->setLastModifiedBy($_SESSION['Name']);
    $PHP_Excel->getProperties()->setTitle("Office 2007 XLSX Document");
    $PHP_Excel->getProperties()->setSubject("Office 2007 XLSX Document");
    $PHP_Excel->getProperties()->setDescription("Student Record Document for Office 2007 XLSX");

    $PHP_Excel->getActiveSheet()->setTitle('Student Record');

    header("Content-Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
    header("Content-Disposition: attachment;filename=" . $Excel_ID . "-student-records.xls");
    header("Cache-Control: max-age=0");

    $PHP_Excel_Writer = new PHPExcel_Writer_Excel2007($PHP_Excel);
    $PHP_Excel_Writer->save("php://output");