Generic hashtable method doesn't work correctly in C#

I am trying to implement a hashtable in C#. Here's what I have so far:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace GenericHashMap.hashtable
{
    class GenericHashtable<T>
    {

        private List<Node<T>> array;
        private int capacity;

        public GenericHashtable(int capacity)
        {
            this.capacity = capacity;
            array = new List<Node<T>>(capacity);
            for (int i = 0; i < capacity; i++)
            {
                array.Insert(i, null);
            }
        }

        public class Node<E>
        {
            private E info;
            private Node<E> next;

            public Node(E info, Node<E> next)
            {
                this.info = info;
                this.next = next;
            }

            public E Info
            {
                get
                {
                    return this.info;
                }
                set
                {
                    this.info = value;
                }
            }

            public Node<E> Next
            {
                get
                {
                    return this.next;
                }
                set
                {
                    this.next = value;
                }
            }
        }

        public bool IsEmpty()
        {
            if (array.Count == 0)
            {
                return true;
            }
            return false;
        }

        public void Add(T element)
        {
            int index = Math.Abs(element.GetHashCode() % capacity);
            Node<T> ToAdd = new Node<T>(element, null);
            Console.WriteLine("index = " + index);

            if (array.ElementAt(index) == null)
            {
                array.Insert(index, ToAdd);
                Console.WriteLine("The element " + array.ElementAt(index).Info.ToString() + " was found at index " + index);
            }
            else
            {
                Node<T> cursor = array.ElementAt(index);
                while (cursor.Next != null)
                {
                    cursor = cursor.Next;
                }
                if (cursor.Next == null)
                {
                    cursor.Next = ToAdd;
                    Console.WriteLine("The element " + array.ElementAt(index).Info.ToString() + " was found at index " + index);
                }
            }
        }

        public bool Search(T key)
        {
            int index = Math.Abs(key.GetHashCode() % capacity);
            Console.WriteLine("Index = " + index);
            Console.WriteLine("The element " + array.ElementAt(index).Info.ToString());

            if (array.ElementAt(index) == null)
            {
                return false;
            }
            else
            {
                if (array.ElementAt(index).Equals(key))
                {
                    Console.WriteLine("The element " + key + "exists in the map at index " + index);
                    return true;
                }
                else
                {
                    Node<T> cursor = array.ElementAt(index);
                    while (cursor != null && !(cursor.Info.Equals(key)))
                    {
                        cursor = cursor.Next;
                    }
                    if (cursor.Info.Equals(key))
                    {
                        Console.WriteLine("The " + key + "exists in the map");
                        return true;
                    }
                }
            }

            return false;
        }

        public void PrintElements()
        {
            for (int i = 0; i < capacity; i++)
            {
                Node<T> cursor = array.ElementAt(i);
                while (cursor != null)
                {
                    Console.WriteLine(cursor.Info.ToString());
                    cursor = cursor.Next;
                }
            }
        }
    }
}

Now, I add the following strings in the table:

GenericHashtable<string> table = new GenericHashtable<string>(11);
            table.Add("unu"); -> index 3
            table.Add("doi"); -> index 0
            table.Add("trei"); -> index 6
            table.Add("patru"); -> index 7
            table.Add("cinci"); -> index 2
            table.Add("sase"); -> index 0

Now, everything's fine, the elements are added. But when I'm trying to search the element "unu" it is not found because it's index is not 3 anymore, it's 5. The index for "trei" is not 6, it's 7... I don't understand why the elements are changing their indexes. I suppose that something is wrong when the elements are added in the Add() method, but I can't figure out myself what. Any answers?