namespace prefix "web" is not declared

Calling a soap web service in plslql, any help would be highly appreciated

 soap request:  <soapenv:Envelope
 xmlns:soapenv="http://ift.tt/sVJIaE"
 xmlns:web="http://ift.tt/18TcHUI">    <soapenv:Header/>   
 <soapenv:Body>
       <web:doThirdPartyPaymentRequest>
          <web:productType>ATF30M</web:productType>
          <web:purchaseDateTime>27-AUG-14</web:purchaseDateTime>
          <web:premiumAmount>1000</web:premiumAmount>
          <web:mtnBranchCode>CONSC</web:mtnBranchCode>
          <web:certificateNumber>1234</web:certificateNumber>
          <web:MSISDN>7659873453</web:MSISDN>
       </web:doThirdPartyPaymentRequest>    </soapenv:Body> </soapenv:Envelope>

response:

00

response extraction:

 WITH t AS (SELECT xmltype(soap_resp_msg) xcol FROM dual)    SELECT
 extractValue(xcol,'/soapenv:Envelope/soapenv:Header/soapenv:Body/web:doThirdPartyPaymentResponse/responseCode'
                          ,'xmlns:SOAPENV="http://ift.tt/sVJIaE"
       xmlns:ns1="http://ift.tt/18TcHUI"
           xmlns:web="http://ift.tt/18TcHUI"
           xmlns="http://ift.tt/18TcHUI"') into result_ from t;

Error:

ORA-31011: XML parsing failed
ORA-19202: Error occurred in XML processing
LPX-00234: namespace prefix "web" is not declared
Error at line 1
ORA-06512: at "SYS.XMLTYPE", line 272
ORA-06512: at line 1
ORA-06512: at "IFSAPP.MINS_IFS_INT", line 59
ORA-06512: at line 3