JaxB Unmarshal Exception: javax.xml.bind.UnmarshalException: unexpected element. Where have i gone wrong?

I have two bean directories, one for request beans and the other for response beans, each containing their own ObjectMapper class.

I was able to succecssfully marshall my XML Beans (for the request) to a XML String before sending it off using the following below.

    JAXBElement<RequestblockType> requestblock = objectFactory.createRequestblock(requestblockType);
    m.marshal(requestblock, writer);
    // output string to console
    byte[] bytes = writer.toString().getBytes(Charset.forName("UTF-8"));

I got my response back from server as an xml string and now trying to unmarshall back into my objects.

    JAXBContext jaxbContext = JAXBContext.newInstance(ResponseblockType.class);
    StringReader reader = new StringReader(xmlString);
    jaxbContext.createUnmarshaller().unmarshal(reader); //this line throws Exception
    um.unmarshal(reader);

On the line specified i get following exception:

javax.xml.bind.UnmarshalException: unexpected element (uri:"", local:"responseblock"). Expected elements are <{}responseblockType>

Below is my XML and the top level bean class which is off the most importance

<?xml version="1.0" encoding="UTF-8"?>
<responseblock version="3.67">
  <requestreference>X5727835</requestreference>
   <response type="AUTH">
  <merchant>
     <merchantname>Merchant1</merchantname>
     <orderreference>8900001233</orderreference>
     <tid>12341234</tid>
     <merchantnumber>00000000</merchantnumber>
     <merchantcountryiso2a>GB</merchantcountryiso2a>
  </merchant>
  <transactionreference>3-9-1598316</transactionreference>
  <timestamp>2014-08-18 11:56:40</timestamp>
  <acquirerresponsecode>00</acquirerresponsecode>
  <operation>
     <accounttypedescription>ECOM</accounttypedescription>
  </operation>
  <settlement>
     <settleduedate>2014-08-18</settleduedate>
     <settlestatus>0</settlestatus>
  </settlement>
  <billing>
     <amount currencycode="USD">3698</amount>
     <payment type="VISA">
        <issuer>Test Issuer1</issuer>
        <pan>1234123412341234</pan>
        <issuercountry>US</issuercountry>
     </payment>
     <dcc enabled="0" />
  </billing>
  <authcode>TEST</authcode>
  <live>0</live>
  <error>
     <message>Ok</message>
     <code>0</code>
  </error>
  <security>
     <postcode>0</postcode>
     <securitycode>2</securitycode>
     <address>0</address>
  </security>

package com.test.adapter.payment.test1.client.model.beans.responses;

import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "responseblockType")
@XmlRootElement
public class ResponseblockType {

@XmlElement(required = true)
protected String requestreference;
@XmlElement(required = true)
protected ResponseType response;
@XmlAttribute(name = "version")
protected String version;

public String getRequestreference() { return requestreference; }
public void setRequestreference(String value) { this.requestreference = value; }
public ResponseType getResponse() { return response; }
public void setResponse(ResponseType value) { this.response = value; }
public String getVersion() { return version; }
public void setVersion(String value) { this.version = value;  }

}

Can anybody let me know where im going wrong? I can supply more information if possible. I saw from other post that adding an @XMLRootElement to my top level bean response class could help but it hasnt. Beside i didnt have to do this for my request when marshalling.