The data overlapping is happening while multiple users access the website.

public static class Read
    {
        private static SqlConnection DataConnection;
        private static SqlDataAdapter DataAdapter;
        private static SqlCommand DataCommand;
        private static DataTable objDataTable;

        static Read()
        {
            DataConnection = new SqlConnection(ConfigurationManager.ConnectionStrings["testDB"].ConnectionString);
            DataCommand = new SqlCommand();
            objDataTable = new DataTable();
            DataAdapter = new SqlDataAdapter();
            DataCommand.Connection = DataConnection;
            DataAdapter.SelectCommand = DataCommand;
        }

        public static DataTable GetBranchesOfRestaurant(int RestaurantId, out string Error)
        {
            Error = string.Empty;
            objDataTable.Clear();
            objDataTable = new DataTable();
            DataCommand.CommandText = "GetBranchesOfRestaurant";
            DataCommand.Parameters.AddWithValue("@RestaurantId", RestaurantId);
            DataCommand.CommandType = CommandType.StoredProcedure;
            try
            {
                if (DataConnection.State != ConnectionState.Open)
                    DataConnection.Open();
                DataAdapter.Fill(objDataTable);
            }
            catch (Exception ex)
            {
                Error = ex.Message;
            }
            finally
            {
                DataCommand.Parameters.Clear();
                DataConnection.Close();
            }
            return objDataTable;
        }
}