Amortization schedule: monthlyprincipal not correctly calculated

I am trying to calculate the Amortization Schedule. The monthly Payments are being calculated in a separate method monthlyPayments() . I compared it with a Amortization Schedule calculator online and the problem is while the principle balance(newPrincipleBalance), monthlyInterest , EMI(monthly payments) are being calculated correctly , the monthlyPrincipal is not. It keeps decreasing instead of increasing. What can I do to correct it?


    {
            double principal = 10000;
            double rate =0;
            double EMI;
            double monthlyInterest;
            double monthlyPrincipal;
            double newPrincipalBalance;

           
            for (int i = 0; i <= 24; i++)
            {

                Console.WriteLine("principal " + principal);
                EMI = Math.Round(monthlyPayments(principal, 5, 2));
                Console.WriteLine("EMI " + EMI);

                monthlyInterest = (principal * rate) / 12;
                monthlyInterest = Math.Round((principal * 5 / 100) / 12);
                Console.WriteLine("monthlyInterest " + monthlyInterest);

                monthlyPrincipal = Math.Round(EMI - monthlyInterest);
                Console.WriteLine("monthlyPrincipal " + monthlyPrincipal);

                newPrincipalBalance = Math.Round(principal - monthlyPrincipal);
                Console.WriteLine("newPrincipalBalance " + newPrincipalBalance);
                Console.WriteLine("===================================");
                principal = newPrincipalBalance;
            }   
}
     public static double monthlyPayments(double principal, double rate, int years)
        {
            rate = rate / 1200;
            years = years * 12;

            double F = (double)Math.Pow((double)(1 + rate), years);
            return principal * (rate * F) / (F - 1);

        }