Modify xmlAttribute Name like xsi:type

Checked i am getting this following result only. But how to add xsi in front of type attribute. I am using .net 2012.  soap ui 5.2.1

Request:

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:web="web:webservice.com">
   <soapenv:Header/>
   <soapenv:Body>

<CancelRequest>
         <arg0>
            <UserName>?</UserName>    

            <PhoneNo> ?</PhoneNo>
         </arg0>

</CancelRequest>

</soapenv:Body>
</soapenv:Envelope>

Response:

<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
   <s:Body xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">

<cancelResponse>
         <cancelResult>        
               <data type="xsd:boolean">false</data>
         </cancelResult>
  </cancelResponse>

 </s:Body>
</s:Envelope>