unable to update value to xml file in windows phone 8

I want to set the attributes pro_id and prod_xml to empty whenever I press on unfavorite icon from application bar. After all, the values were to set to empty however, it also add one more root element to the xml file like this

<?xml version="1.0" encoding="utf-8"?>
<favorites>
  <favorite id="1" pro_id="" prod_xml="" />
  <favorite id="2" pro_id="" prod_xml="" />
  <favorite id="3" pro_id="" prod_xml="" />
  <favorite id="4" pro_id="" prod_xml="" />
</favorites> />
</favorites>

Here my code to do this

public void UnwriteXML(string pro_id)
        {
            var storage = IsolatedStorageFile.GetUserStoreForApplication();
            fileName = "Favorite\\Favorite.xml";
            XDocument docx = null;
            using (IsolatedStorageFileStream isoStreamx = new IsolatedStorageFileStream(fileName, FileMode.Open, storage))
            {

                 docx = XDocument.Load(isoStreamx);
                foreach (var item in (from item in docx.Descendants("favorite")
                                      where item.Attribute("pro_id").Value.Equals(pro_id)
                                      select item).ToList())
                {

                    item.Attribute("pro_id").SetValue("");
                    item.Attribute("prod_xml").SetValue("");

                }


                //First way
                isoStreamx.Position = 0;
                docx.Save(isoStreamx);
            }  

        }

I followed exactly the same to question post from here updating an existing xml file in Windows Phone by setting isoStream to position 0 because I think he have a problem like me, but the problem is still the same, I don't understand what's wrong with this.