How to comapre a sharepoint list and a c#list

I have a sharepoint calender list which contains columns like orderID, orderdesc etc. the data into calender list is updated from a csv file in item added and item updated event. I am facing issue in item updating, if the order id is already present in calneder list, it should be updated. in y code, it is creating a new entry rather than updating. Where am i going wrong. Here is my item updating event

 public override void ItemUpdated(SPItemEventProperties properties)
    {
        base.ItemUpdated(properties);
        try
        {
            SPWeb web = properties.Web;
            SPList calendarList = web.Lists.TryGetList(CalendarListTitle);
            SPQuery changeorderquery = new SPQuery();
            changeorderquery.Query =
                "<Query /><ViewFields><FieldRef Name='ChangeOrderNumber' /></ViewFields><QueryOptions />";
            SPListItemCollection changeOrderCollection = calendarList.GetItems(changeorderquery);

            StreamReader content;
            if (web.GetFile(properties.AfterUrl) != null)
            {
                SPFile file = web.GetFile(properties.AfterUrl);
                content = new StreamReader(file.OpenBinaryStream());
                var data = Parse(content);

                foreach (var fieldValues in data)
                {
                    foreach (SPListItem changeOrder in changeOrderCollection)
                    {
                        for (int i = 0; i < data.Count; ++i)
                        {
                            if (changeOrder["ChangeOrderNumber"].ToString() == data[i][0]) // if the changeorder exists
                            { 
                                var itemid = changeOrder.ID;
                                SPListItem item = calendarList.GetItemById(itemid);
                                //foreach (SPListItem item in calenderitems)
                                //{
                                item["ChangeOrderNumber"] = fieldValues[0];
                                item["Requestor"] = fieldValues[1];
                                item["ImplementationStartDate"] = fieldValues[2];
                                item["ImplementationEndDate"] = fieldValues[3];
                                item["COStatus"] = fieldValues[4];
                                item["Assignee"] = fieldValues[5];
                                item["OrderSummary"] = fieldValues[6];
                                item["OrderDescription"] = fieldValues[7];
                                item["Justification"] = fieldValues[8];
                                item["COURL"] = fieldValues[9];

                                var orderSummary = item["OrderDescription"].ToString();
                                string eventType = GetEventType(orderSummary);
                                if (eventType != null)
                                {
                                    item["EventType0"] = eventType;
                                }
                                else
                                {
                                    item["EventType0"] = "";
                                }
                                item.Update();

                            }
                             if (changeOrder["ChangeOrderNumber"].ToString() != data[i][0])
                            {
                                SPListItem item = calendarList.Items.Add();
                                item["ChangeOrderNumber"] = fieldValues[0];
                                item["Requestor"] = fieldValues[1];
                                item["ImplementationStartDate"] = fieldValues[2];
                                item["ImplementationEndDate"] = fieldValues[3];
                                item["COStatus"] = fieldValues[4];
                                item["Assignee"] = fieldValues[5];
                                item["OrderSummary"] = fieldValues[6];
                                item["OrderDescription"] = fieldValues[7];
                                item["Justification"] = fieldValues[8];
                                item["COURL"] = fieldValues[9];

                                var orderSummary = item["OrderDescription"].ToString();
                                string eventType = GetEventType(orderSummary);
                                if (eventType != null)
                                {
                                    item["EventType0"] = eventType;
                                }
                                else
                                {
                                    item["EventType0"] = "";
                                }

                                item.Update();
                            }
                            break;

                        }
                        break;
                    }
                   // break;
                }
            }
        }

        catch (Exception ex)
        {
            throw new Exception("failed to update");
        }
    }


}