I am struggling with the maxSubmatrixSum(matrix). I am new to Object Orientated and I thought I had a good understanding of it but clearly not. Why do I print 9 instead of 33?

using System;

namespace Test
{
    class Program
    {
//You still have too many for loops in the max sum matrix one, you just need to traverse the 
     //matrix find the sum as you go and compare it with the current max
     //If sum is greater than the current sum, you update the sum and change the matrix


    static void Main(string[] args)
    {
        //Function to find maximum sum submatrix, we need to use [,],→ character for our int
        static void maxSubmatrixSum(int[,] matrix)
        {

            // Stores the number of rows and columns in the matrix
            int r = matrix.GetLength(0);
            int c = matrix.GetLength(1);

            // initiates maximum submatrix sum to zero
            int maxSubmatrix = 0;

            // Makes each row the first in the array
            for (int i = 0; i < r; i++)
            {
                // Makes each column the first in the array
                for (int j = 0; j < c; j++)
                {
                    // Stores the sum of submatrix having,→ topleft index(i, j) and bottom right index(k, l)
                    int sumSubmatrix = 0;

                    // iterate the submatrix row-wise and,→ calculate its sum
                    for (int m = i; m <= i; m++)
                    {
                        for (int n = j; n <= j; n++)
                        {
                            sumSubmatrix += matrix[i, j];
                        }
                    }

                    // Update the maximum sum
                    maxSubmatrix
                    = Math.Max(maxSubmatrix,
                    sumSubmatrix);

                }
            }

            // Print the answer
            Console.WriteLine(maxSubmatrix);
        }

        int[,] matrix = { { 0, 2, 4, 0, 9, 5 },
    { 7, 1, 3, 3, 2, 1 },
    { 1, 3, 9, 8, 5, 6 },
    { 4, 6, 7, 9, 1, 0 } };

        maxSubmatrixSum(matrix);

    }
}