I have exposed my REST API service using WCF Service Library and started by console application. when I try to consume the service from client ( another console application)
Your XML namespaces are wrong. I don't have time to correct it for you, but needs to be in the "http://www.test.com/Enrollment" namespace according to your data contract.
Your POST payload should be :
<Enroll xmlns="http://www.test.com/Enrollment">
<ClientId>000</ClientId>
<AccountNumber>123</AccountNumber>
<TaxId>123</TaxId>
<TaxType>123</TaxType>
<EmailAddress>123</EmailAddress>
<Pin>123</Pin>
<State>122</State>
</Enroll>