How to remove namespace during XML serialization in C#?

<CREATEPMDEBTORMANDATE_FSFS_REQ>
	<FCUBS_HEADER
		xmlns="http://pmts.ofss.com/ws/PMDebtorMandate">
		<SOURCE>DDS</SOURCE>
		
	</FCUBS_HEADER>
	<FCUBS_BODY
		xmlns="http://pmts.ofss.com/ws/PMDebtorMandate">
		<Dr-Dd-Mandate-Master-Full>
			<CR_AC_CCY>AED</CR_AC_CCY>
			
		</Dr-Dd-Mandate-Master-Full>
	</FCUBS_BODY>
</CREATEPMDEBTORMANDATE_FSFS_REQ>

<CREATEPMDEBTORMANDATE_FSFS_REQ>
	<FCUBS_HEADER>
		<SOURCE>DDS</SOURCE>
		
	</FCUBS_HEADER>
	<FCUBS_BODY>
		<Dr-Dd-Mandate-Master-Full>
			<CR_AC_CCY>AED</CR_AC_CCY>
			
		</Dr-Dd-Mandate-Master-Full>
	</FCUBS_BODY>
</CREATEPMDEBTORMANDATE_FSFS_REQ>

XmlDocument xmlDoc = new XmlDocument();
           XPathNavigator nav = xmlDoc.CreateNavigator();

           XmlSerializer ser = null;
           using (XmlWriter writer = nav.AppendChild())
           {
               XmlSerializerNamespaces ns = new XmlSerializerNamespaces();
               ns.Add(string.Empty,string.Empty);
               if (Type == "CreateMandate")
               {
                   ser = XmlSerializerCache.Create(objList.GetType(), new XmlRootAttribute("CREATEPMDEBTORMANDATE_FSFS_REQ"));
               }
               ser.Serialize(writer, objList, ns);

           }
           string retXML = xmlDoc.InnerXml;

           xmlDoc = null;
           nav = null;

           return retXML;