无法在PHP中将MySQL数据下载到Excel

I want to export my mysql query result to excel sheet. for that, i used the code given in Export MySQL data to Excel in PHP It is working when i check in console but not downloading. Pls help me. I dont know why it is not downloading. Here is my code:

$startDate = $_POST['fromDate'];
    $endDate = $_POST['toDate'];

    $db = new Db();
    $data = $db -> select("SELECT od.Id,mm.ProductName,oi.Quantity,od.OrderDate,od.FirstName,od.LastName,od.Address, od.ZipCode, od.EmailID, od.ContactNumber FROM tw_orderdetails od JOIN tw_ordereditems oi ON oi.OrderID = od.Id JOIN tw_marketingmaterials mm on mm.Id = oi.ProductID WHERE date(od.OrderDate) BETWEEN ".$db->quote($startDate)." AND ".$db->quote($endDate)."");

    $fieldNames = array('Order ID','ProductName','Quantity','OrderDate','FirstName','LastName','Address','ZipCode','EmailID','ContactNumber');

    $filename = "excelfilename";  
    $file_ending = "xls";
    //header info for browser
    header("Content-Type: application/xls");    
    header("Content-Disposition: attachment; filename=$filename.xls");  
    header("Pragma: no-cache"); 
    header("Expires: 0");
    /*******Start of Formatting for Excel*******/   
    //define separator (defines columns in excel & tabs in word)
    $sep = "\t"; //tabbed character
    //start of printing column names as names of MySQL fields
    for ($i = 0; $i < count($fieldNames) ; $i++) {
        echo $fieldNames[$i] . "\t";
    }
    print("
");    
    //end of printing column names  
    //start while loop to get data
    foreach ($data as &$row) {
        $schema_insert = "";
        foreach ($row as &$value)
        {
            if(!isset($value))
                $schema_insert .= "NULL".$sep;
            elseif ($value != "")
                $schema_insert .= "$value".$sep;
            else
                $schema_insert .= "".$sep;
        }

        $schema_insert = str_replace($sep."$", "", $schema_insert);
        $schema_insert = preg_replace("/
|
|
|/", " ", $schema_insert);
        $schema_insert .= "\t" ;
        print(trim($schema_insert));
        print "
";
    }