Return JSON response in WCF REST services

[OperationContract]
       [WebInvoke(UriTemplate = "GetAppointments/?companyId={companyId}&appointmentDate={appointmentDate}", Method = "GET", RequestFormat = WebMessageFormat.Json, ResponseFormat = WebMessageFormat.Json, BodyStyle = WebMessageBodyStyle.Bare)]
     GetAppointmentList GetAppointment(Guid companyId, string appointmentDate);

public GetAppointmentList GetAppointment(Guid companyId, string appointmentDate)
{     
    SQLDataContext context = new SQLDataContext();
    var getappointment = context.GetAppointmentTimings(companyId,appointmentDate);
    GetAppointmentList getappointmentlist = new GetAppointmentList();
    getappointmentlist.AppointmentList = new List<company>().ToList();         
    foreach (var r in getappointment.ToList())
    {
        Company company = new Company();
        company.CompanyId = r.CompanyId;
        company.CompanyName = r.CompanyName;
        company.BreakStartTime = r.BreakStartTime + ":" + "00";
        company.BreakEndTime = r.BreakEndTime + ":" + "00";
        company.Interval = r.Interval;
        company.AppointmentStartTime = r.AppointmentStartTime;
        company.AppointmentEndTime = r.AppointmentEndTime;
        getappointmentlist.AppointmentList.Add(company);
    }

    return getappointmentlist;
}

<system.serviceModel>
    <services>
      <service name="Appointments.CompanyService" behaviorConfiguration="SampleCompSvcBehavior">
        <host>
          <baseAddresses>
            <add baseAddress="http://localhost:8732/SampleCompService"/>
          </baseAddresses>
        </host>

        <endpoint address="http://localhost:8732/SampleCompService/json" binding="webHttpBinding" contract="Appointments.ICompanyService" behaviorConfiguration="SampleCompSvcWebBehavior" bindingConfiguration="hk"/>

<endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange"/>
     </service>
   </services>
   <bindings>
     <webHttpBinding>
       <binding name="hk">
         <security mode="None"></security>
       </binding>
     </webHttpBinding>
   </bindings>
   <behaviors>
     <serviceBehaviors>
       <behavior name="SampleCompSvcBehavior">

         <serviceMetadata httpGetEnabled="True"/>

         <serviceDebug includeExceptionDetailInFaults="false"/>
       </behavior>
     </serviceBehaviors>
     <endpointBehaviors>
       <behavior name="SampleCompSvcWebBehavior">
         <webHttp helpEnabled="true" defaultOutgoingResponseFormat="Json" automaticFormatSelectionEnabled="true" />
       </behavior>
     </endpointBehaviors>
   </behaviors>
   <serviceHostingEnvironment aspNetCompatibilityEnabled="true" multipleSiteBindingsEnabled="true"/>
 </system.serviceModel>