Why when using a ui button script with ui toggle to interact with another script it's not working good ?

I have in the Hierarchy a Canvas and as a child i have a ui button and ui toggle. On the button i attached a new script:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class GenerateObjectsButton : MonoBehaviour
 {
     private InstantiateObjects instantiateobjects;
     private bool toggleOnOf;
     public Toggle toggle;
 
     private void Start()
     {
         instantiateobjects = new InstantiateObjects();
         toggle.onValueChanged.AddListener((value) =>
             {
                 MyListener(value);
             });
     }
 
     public void MyListener(bool value)
     {
         if (value)
         {
             //do the stuff when the toggle is on
             toggleOnOf = true;
         }
         else
         {
             //do the stuff when the toggle is off
             toggleOnOf = false;
         }
     }
 
     public void OnButton()
     {
         if (toggleOnOf == false)
         {
             instantiateobjects.generateObjectOnTerrain();
         }
         else
         {
             instantiateobjects.DestroyObjects();
             instantiateobjects.generateObjectOnTerrain();
         }
 
     }
 }
 

And this is the InstantiateObjects script:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 //[ExecuteInEditMode]
 public class InstantiateObjects : MonoBehaviour
 {
     public GameObject prefab;
     public Terrain terrain;
     public float yOffset = 0.5f;
     public int objectsToInstantiate;
     public bool parent = true;
     public bool randomScale = false;
     public float setRandScaleXMin, setRandScaleXMax;
     public float setTandScaleYMin, setTandScaleYMax;
     public float setTandScaleZMin, setRandScaleZMax;
     public bool generateNew;
 
     private float terrainWidth;
     private float terrainLength;
     private float xTerrainPos;
     private float zTerrainPos;
     private int numberOfObjectsToCreate;
     private GameObject objInstance;
     private GameObject[] createdObjects;
     private string objname;
 
     public void Start()
     {
         //Get terrain size
         terrainWidth = terrain.terrainData.size.x;
         terrainLength = terrain.terrainData.size.z;
 
         //Get terrain position
         xTerrainPos = terrain.transform.position.x;
         zTerrainPos = terrain.transform.position.z;
 
         numberOfObjectsToCreate = objectsToInstantiate;
 
         objname = prefab.name;
         MyCustomEditor.TagsAndLayers.AddTag(objname);
 
         generateNew = false;
         generateObjectOnTerrain();
     }
 
     public void Update()
     {
         
     }
 
     public void DestroyObjects()
     {
         if (createdObjects != null && createdObjects.Length > 0)
         {
             for (int i = 0; i < createdObjects.Length; i++)
             {
                 DestroyImmediate(createdObjects[i]);
             }
             createdObjects = new GameObject[0];
         }
     }
 
     public void generateObjectOnTerrain()
     {
         for (int i = 0; i < objectsToInstantiate; i++)
         {
             //Generate random x,z,y position on the terrain
             float randX = UnityEngine.Random.Range(xTerrainPos, xTerrainPos + terrainWidth);
             float randZ = UnityEngine.Random.Range(zTerrainPos, zTerrainPos + terrainLength);
 
             float yVal = Terrain.activeTerrain.SampleHeight(new Vector3(randX, 0, randZ));
 
             //Generate random x,y,z scale on the terrain
             float randScaleX = Random.Range(setRandScaleXMin, setRandScaleXMax);
             float randScaleY = Random.Range(setTandScaleYMin, setTandScaleYMax);
             float randScaleZ = Random.Range(setTandScaleYMax, setRandScaleZMax);
 
             //Apply Offset if needed
             yVal = yVal + yOffset;
 
             //Generate the Prefab on the generated position        
             objInstance = Instantiate(prefab, new Vector3(randX, yVal, randZ), Quaternion.identity);
 
             if (randomScale == true)
                 objInstance.transform.localScale = new Vector3(randScaleX, randScaleY, randScaleZ);
 
             if (parent)
                 objInstance.transform.parent = this.transform;
 
             objInstance.tag = objname;
         }
 
         createdObjects = GameObject.FindGameObjectsWithTag(objname);
     }
 }

What it does now when running the game is creating new gameobjects. Now what i want to do is:

When i click the button depending on what state the toggle is create new gameobjects. If the toggle is true then first destroy all created gameobjects and create new ones.

If the toggle is set to false and i click the button then just create moew new gameobjects don't destroy the others.

But i can't make the GenerateObjectsButton script to work good with the InstantiateObjects script.

First each time i click the button i'm getting null exception in the script InstantiateObjects on the line:

 createdObjects = GameObject.FindGameObjectsWithTag(objname);

createdObjects is null. And another problem is the logic in the GenerateObjectsButton is not working good i need to change the toggle to false true twice to get to the DestroyObjects method.

But the main goal is using the button according to the toggle state to create new gameobjects with/without destroying the old ones.