how to disable function that have InvokeRepeating

Hi, sorry if this question is duplicate, but I did my best to find the salutation by my self but I didn't found a solution to solve my problem.

I have code that insatiate object by InvokeRepeating, and what I want is, if the object touch collider2d the instantiation have to stop, and this is what I did.

Script B (Control)

 void OnTriggerEnter2D (Collider2D collider2d)
     {
 
         if (collider2d.tag == "Checkpoint") 
         {
             point++;
             scoreText.text = point + "";
             Debug.Log ("CheckPoint");
         }
 
 
         if (collider2d.tag == "GameOver") 
         {
             Debug.Log ("touched");
             Destroy (player);
 
             scoreText.text = "0";
 
             spawnCircle sc = GetComponent<spawnCircle>();
             sc.stopGame();
 
 
         }
 
     }

Script A (spawnCircle)

 public static bool theGameisActive = true;
 
 void Start () {
         
         if (theGameisActive == true)
         {
             Vector3 middle = new Vector3 (0.0f, 0.0f, 0.0f);
 
             int objectIndex = Random.Range (0, circleSpawning.Length);
 
             Instantiate (circleSpawning [objectIndex], middle, Quaternion.Euler (new Vector3 (0, 0, Random.Range (180, 90))));
 
             InvokeRepeating ("circleSpawn", delayTimer, delayTimer);
 
             Debug.Log ("The game is just started");
         }    
     }
 
 void circleSpawn ()
     {
 
         if (theGameisActive == true)
         {
             Vector3 middle = new Vector3 (0.0f, 0.0f, 0.0f);
 
             int objectIndex = Random.Range (0, circleSpawning.Length);
 
             Instantiate (circleSpawning [objectIndex], middle, Quaternion.Euler (new Vector3 (0, 0, Random.Range (0, 360))));
         }
     
     }
 
 public void stopGame ()
     {        
         theGameisActive = false;
         Debug.Log ("stopGame");        
     }
 

When I did this code I get an error: NullReferenceException: Object reference not set to an instance of an object Control.OnTriggerEnter2D (UnityEngine.Collider2D collider2d) (at Assets/scripts/Control.cs:56)

Can I find someone help me to solve this problem please

Thanks,