How to Append CSV file without merging the previous values

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C#

.NET

I have written a code for converting list elements to CSV file.
It works fine.
But the thing is that while appending with then new datas the last element of the previous data in the CSV gets concatenated with the newly formed datas.

Here is my code. Please separate the datas in a new line

string fileName = System.Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments) + "\\CSV.csv";

            TextWriter writer = new StreamWriter(fileName,true);
          
            List<string> stringList = new List<string>();
            Console.Write("Enter the number of elements in the list: ");
            int listSize;
            int.TryParse(Console.ReadLine(),out listSize);
            Console.WriteLine("Enter {0} elements one by one: ",listSize); 
            for (int index = 0; index < listSize; index++)
            {
                stringList.Add(Console.ReadLine());
            }
            Console.Write("\nList elements:\n\n");
            foreach (var items in stringList)
            {
                Console.WriteLine(items);
            }
            string csvString = string.Join(",", stringList.ToArray());
            Console.WriteLine("\nCSV Output");
            Console.WriteLine("\n"+csvString);
            writer.Write(csvString);
            writer.Close();
            Console.ReadLine();