unity2d inventory old style (like final fantasy) storing items amount issue C#

-2 down vote favorite I was working in an simple 2d rpg game and I was working on a simple inventory system with only UI TEXT (not icons).

For example, when I open a chest and find 1 potion and then open another chest and find another potion I need to destroy that potion and increase the quantity of the first potion by 1, but it doesn't work correctly.

When I use random.range and put multiple items to randomise, it doesn't work, but when I use only one item it works (ex random.range (0.0) )!

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine.UI;
 
 public class inventoryTest : MonoBehaviour
 {
     public Transform panel;
     public List<Item> Inventory = new List<Item>();
     public ItemDatabase data;
     public GameObject Menu;
     public bool pressed;
 
     public Text testText;
 
     private void Start()
     {
         data = GameObject.FindGameObjectWithTag("database").GetComponent<ItemDatabase>();
     }
 
     private void Update()
     {
         for (int i = 0; i < Inventory.Count; i++)
         {
             testText.name = Inventory[i].Itemname;
             testText.text = Inventory[i].Itemname + " : " + Inventory[i].capacity;
         }
 
         if (Input.GetKeyDown(KeyCode.I) && !pressed)
         {
             pressed = true;
             Menu.SetActive(true);
             Time.timeScale = 0;
         }
         else if (Input.GetKeyDown(KeyCode.I) && pressed)
         {
             Time.timeScale = 1;
             pressed = !pressed;
             Menu.SetActive(false);
         }
     }
 
     public void CheckForItemExist(int ID, Item item)
     {
         for (int i = 0; i < Inventory.Count; i++)
         {
             if (Inventory[i].ItemId == ID)
             {
                 item = data.items[i];
 
                 //Inventory[i] = new Item(item.ItemId,item.Itemname,item.ItemPower,item.Itemtype,item.capacity) ;
 
                 Inventory[i].capacity = item.capacity;
                 item.capacity += 1;
                 Inventory[i].Itemtype = item.Itemtype;
                 Inventory[i].ItemPower = item.ItemPower;
                 Inventory[i].Itemname = item.Itemname;
                 Inventory[i].ItemId = item.ItemId;
 
                 foreach (Item items in Inventory)
                 {
                     if (Inventory[i] == item)
                     {
                         Inventory.Remove(item);
                         Destroy(testText.gameObject);
                     }
                 }
 
                 break;
             }
         }
     }
 
     private void AddEmpty(Item item)
     {
         for (int i = 0; i < Inventory.Count; i++)
         {
             if (Inventory[i].Itemname == null)
             {
                 Inventory[i] = item;
                 //
 
                 break;
             }
         }
     }
 
     public void DesplayInventory()
     {
         for (int i = 0; i < Inventory.Count; i++)
         {
             Text _text = Instantiate(Resources.Load("Text", typeof(Text)), new Vector2(panel.transform.position.x, panel.transform.position.y * i), Quaternion.identity) as Text;
             testText = _text;
             _text.transform.SetParent(panel);
             _text.transform.localScale = new Vector3(1, 1, 1);
 
             Debug.Log(testText);
 
             break;
         }
     }
 }

and here is the chest script

 using System.Collections;
 using System.Collections.Generic;
 
 public class generateItem : MonoBehaviour
 {
     public Sprite open;
     private inventoryTest inv;
     private test test;
     public bool opened;
     private ItemDatabase data;
 
     private void Start()
     {
         test = GameObject.FindGameObjectWithTag("Player").GetComponent<test>();
         inv = GameObject.FindGameObjectWithTag("Player").GetComponent<inventoryTest>();
         data = GameObject.FindGameObjectWithTag("database").GetComponent<ItemDatabase>();
     }
 
     private void Update()
     {
         if (opened)
         {
             Destroy(this);
         }
     }
 
     private void OnCollisionStay2D(Collision2D other)
     {
         if (other.collider.tag == "Player" && Input.GetKeyDown(KeyCode.Return))
         {
             if (!opened)
             {
                 var value = Random.Range(1, 2);
 
                 inv.CheckForItemExist(value, inv.data.items[value]);
                 inv.Inventory.Add(inv.data.items[value]);
                 inv.DesplayInventory();

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