Implementation of quick sort in C#

I'm currently learning programming for the first time and I've created the following implementation of quick sort in C#. I basically read a very basic overview of how quick sort works recursively and implemented it without looking at any concrete examples of its implementation so that I could learn the most from it.

Could you let me know what you think and where it could be optimized?

class Program
{
    static void Main(string[] args)
    {
        var input = new int[] {  10, 3, 20, 5, 200 };
        QuickSort(0, 0, input.Length-1, input);
        Console.WriteLine("Sorted output: :");
        new List<int>(input).ForEach(x => Console.Write(x + ","));
        Console.ReadLine();
    }

    /// <summary>
    /// sample input: 5 7 3 9 2
    /// same output: 2 3 5 7 9
    /// </summary>
    /// <param name="numbers"></param>
    public static void QuickSort(int pivotIndex, int startIndex, int endIndex, int[] numbers)
    {
        if (startIndex == endIndex) return;

        int pivotNumber = numbers[pivotIndex];

        var lowerThanPivot = new List<int>();
        var higherThanPivot = new List<int>();

        for(int i = startIndex; i <= endIndex; i++)
        {
            if(i != pivotIndex)
            {
                if( numbers[i] <= pivotNumber )
                    lowerThanPivot.Add(numbers[i]);
                else
                    higherThanPivot.Add(numbers[i]);
            }
        }

        // now lets put the pivot number in the correct place
        numbers[startIndex + lowerThanPivot.Count] = pivotNumber;

        // reinsert the numbers lower than pivot in the right place
        int z = startIndex;
        lowerThanPivot.ForEach(x => numbers[z++] = x);

        z++; // *** skip over the new pivot index ***

        // reinsert the numbers higher than pivot in the right place
        higherThanPivot.ForEach(x => numbers[z++] = x);

        // recursively call to sort each remaining elements

        int newLeftPivot = startIndex;
        int newEndLeftIndex = newLeftPivot + lowerThanPivot.Count - 1 ;

        int newRightPivot = lowerThanPivot.Count + 1;
        int newEndRightIndex = newRightPivot + higherThanPivot.Count - 1;


        if(lowerThanPivot.Count> 0)
            QuickSort(newLeftPivot, newLeftPivot, newEndLeftIndex, numbers);

        if(higherThanPivot.Count > 0)
            QuickSort(newRightPivot, newRightPivot, newEndRightIndex, numbers);

    }
}