This problem is created due to [WebInvoke(Method = "*", BodyStyle = WebMessageBodyStyle.Wrapped, ResponseFormat
It is happening you are using ResponseFormat for WebInvoke
So it needs to change below format
[OperationContract]
[WebGet(ResponseFormat = WebMessageFormat.Json)]
[FaultContract(typeof(KenException))]
List<Data> GetAllData(); //Select time
[OperationContract]
[WebInvoke(RequestFormat = WebMessageFormat.Json)]
[FaultContract(typeof(KenException))]
DataInsertData(Data user);//Insert Time
Thanks