WCFErr No overload for method 'NameOfViod' takes x arguments

Question

Ok this is my first look and WCF so I am hoping this is a simple fix. This is my code

namespace Bibliotheca.InstallMon :
{
  class InstallMonService : IInstallMon

 {

        public void WriteXMLdata(String p_name, String appv, String date_time, String u_name, String IPAddress, String m_name)
        {

           SomeCode;
           
        }

}

And this is my service

namespace Bibliotheca.InstallMon
{
    [XmlSerializerFormat]

    [ServiceContract]
    public interface IInstallMon
    {

        [OperationContract]

       
       void WriteXMLdata(String p_name, String appv, String date_time, String u_name, String IPAddress, String m_name);

    }
}
 

I then call it from a client app like so.

InstallMonClient client = new InstallMonClient(); 

IInstallMon.WriteXMLdata("string", "string", "string", "string", "string", "string");

But unfortunately I get the above error where am I going wrong :(.

Thanks for your help.