WCF - MessageContract members (MessageBodyMember) ignored when deserialising - wcf

Question

I am consuming a SOAP service, and successfully receiving a response.
Unfortunately, WCF isn't deserialising the members of the response POCO.
Using Diagnostics Tracing, I get the following error occurring for each member in the Response:
Description An unrecognised element was encountered in the XML during deserialisation which was ignored.
Element :partnerId
Please can you see where I am going wrong?
Here's the code:
Service Contract
[ServiceContract(Namespace = "https://foo.com/services/mediationV1/", ConfigurationName = "IPlatformPortType")]
public interface IPlatformPortType
{
[OperationContract(Action = "https://foo.com/services/foo_bar_HeartBeatV1/", ReplyAction = "*")]
HeartBeatResponse SendHeartBeat(HeartbeatRequest request);
}
POCO Request
[MessageContract(IsWrapped = true,
WrapperName = "foo_bar_HeartBeatRequest",
WrapperNamespace = "https://foo.com/schemas/fooV1/")]
public class HeartbeatRequest
{
[MessageBodyMember(Namespace = "https://foo.com/schemas/fooV1/", Order = 0)]
public string transactionId { get; set; }
[MessageBodyMember(Namespace = "https://foo.com/schemas/fooV1/", Order = 2)]
public string partnerId { get; set; }
}
SOAP Request
<s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope" xmlns:a="http://www.w3.org/2005/08/addressing">
<s:Header>
<a:Action s:mustUnderstand="1">https://foo.com/services/foo_bar_HeartBeatV1/</a:Action>
<a:MessageID>urn:uuid:73efa49e-f2b3-4f5d-b750-6784b1becfbc</a:MessageID>
<a:ReplyTo>
<a:Address>http://www.w3.org/2005/08/addressing/anonymous</a:Address>
</a:ReplyTo>
</s:Header>
<s:Body>
<foo_bar_HeartBeatRequest xmlns="https://foo.com/schemas/fooV1/">
<transactionId>f642df34-d328-4d76-9a9f-3cf64bdef71d</transactionId>
<partnerId>bob</partnerId>
</foo_bar_HeartBeatRequest>
</s:Body>
</s:Envelope>
POCO Response
[MessageContract(IsWrapped = true,
WrapperName = "foo_bar_HeartBeatResponse",
WrapperNamespace = "https://foo.com/schemas/fooV1/")]
public class HeartBeatResponse
{
[MessageBodyMember(Namespace = "https://foo.com/schemas/fooV1/", Order = 2)]
public string transactionId { get; set; }
[MessageBodyMember(Namespace = "https://foo.com/schemas/fooV1/", Order = 3)]
public int requestStatus { get; set; }
}
SOAP Response
<soapenv:Envelope xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope">
<soapenv:Header xmlns:wsa="http://www.w3.org/2005/08/addressing">
<wsa:MessageID>urn:uuid:b66497fd-4e95-458c-8772-c8bfc0decb51</wsa:MessageID>
<wsa:Action>urn:mediateResponse</wsa:Action>
<wsa:RelatesTo>urn:uuid:73efa49e-f2b3-4f5d-b750-6784b1becfbc</wsa:RelatesTo>
</soapenv:Header>
<soapenv:Body>
<ns:foo_bar_HeartBeatResponse xmlns:ns="https://foo.com/schemas/fooV1/">
<transactionId>f642df34-d328-4d76-9a9f-3cf64bdef71d</transactionId>
<requestStatus>1</requestStatus>
</ns:foo_bar_HeartBeatResponse>
</soapenv:Body>
</soapenv:Envelope>
Update
As per #TomRedfern's comment, I tried swapping out all the MessageContract attributes with DataContract.
Unfortunately this takes away my ability to notify the seriliaser that the POCO is a wrapper, causing the SOAP to look like the following:
<s:Body>
<SendHeartBeat xmlns="https://foo.com/services/fooV1/">
<request xmlns:b="https://foo.com/schemas/fooV1/" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
<b:transactionId>7085587a-4275-49ad-9aa9-5b413afcbe62</b:transactionId>
<b:partnerId>bob</b:partnerId>
</request>
</SendHeartBeat>
</s:Body>
Notice the name of the node is now the name of the Operation (SendHeartBeat), and it's child node is the parameter name of that operation.
I do not have control over the WSDL, so this will not work.

Answer 1

After a day's worth of trial and error attempts, I've finally got the deserialisation working correctly.
For each of the POCO's members I did the following:
add an XmlElementAttribute.
add the Form parameter to XmlElementAttribute, with value of XmlSchemaForm.Unqualified.
remove the Namespace parameter from the MessageBodyMemberAttribute and add to the XmlElementAttribute.
removed any existing parameters in MessageBodyMemberAttribute.
Here is the correct response POCO:
[MessageContract(IsWrapped = true,
WrapperName = "foo_bar_HeartBeatResponse",
WrapperNamespace = "https://foo.com/schemas/fooV1/")]
public class HeartBeatResponse
{
[MessageBodyMember]
[XmlElement(Form = XmlSchemaForm.Unqualified, Namespace = "https://foo.com/schemas/fooV1/")]
public string transactionId { get; set; }
[MessageBodyMember]
[XmlElement(Form = XmlSchemaForm.Unqualified, Namespace = "https://foo.com/schemas/fooV1/")]
public int requestStatus { get; set; }
}