Not able to update values in a list

 public class TaxBucket
    {
        public int Year { get; set; }
        public List<TaxBucketSub> taxbucketsub { get; set; }

    }
    public class TaxBucketSub
    {
        public int PortfolioID { get; set; }
        public CarryForwards carryforwards { get; set; }
        public CarryForwards buckets { get; set; }
        public CarryForwards currentyearvalue { get; set; }
    }
public class CarryForwards
    {
        public double taxDeduction { get; set; }
        public double interest { get; set; }
        public double dividend { get; set; }
        public double shortTermGains { get; set; }
        public double longTermGains { get; set; }
    }

public static void UpdateTaxBucket(List<TaxBucket> lsttaxbucket, int year, int portnum, string mainitem, string subitem, double value)
       {
           foreach (var bucket in lsttaxbucket.Where(b => b.Year == year))
           {
               foreach (var item in bucket.taxbucketsub.Where(p => p.PortfolioID == portnum))
               {
                   switch (mainitem)
                   {
                       case "buckets":
                           switch (subitem)
                           {
                               case "Interest":
                                   item.buckets.interest = 12;
                                   break;
                               case "Dividend":
                                   item.buckets.dividend =25;
                                   break;
                               case "Short":
                                   item.buckets.shortTermGains = 30;
                                   break;
                               case "Long":
                                   item.buckets.longTermGains =35;
                                   break;
                               case "Tax":
                                   item.buckets.taxDeduction = 50;
                                   break;
                               default:
                                   break;
                           }
                           break;