Bomb not effecting anything.

I created a bomb, i want the bomb to effect the enemy health only if the bomb is in the enemy range. Codes:

1.When the bomb collides with any thing:

 var e : GameObject;
 var radius : float = 3.0;
 var power : float = 300.0;
 var damage : int = 100;
 
 function OnCollisionEnter(c : Collision){
     
     var enemy : GameObject = GameObject.FindWithTag("Enemy");
     
     var explosionPos : Vector3 = transform.position;
     var colliders : Collider[] = Physics.OverlapSphere(explosionPos, radius);
 
     for(var hit : Collider in colliders){
     
     if(hit.gameObject.tag == "Player"){
         
         playerHealth.health -= 75;
         
     }
     if(hit.gameObject.tag == "Enemy"){
     print("work");
     yield WaitForSeconds(3);
     Destroy(gameObject);
     Instantiate(e, transform.position, transform.rotation);
     enemy.SendMessageUpwards("HitEnemy", 15, SendMessageOptions.DontRequireReceiver);
         }
     }
     
     if(c.gameObject.tag == "Player"){
     
         playerHealth.health -= 75;
     }
         
     if(c.gameObject.tag == "Untagged"){
     yield WaitForSeconds(3);
     Instantiate(e, transform.position, transform.rotation);
     Destroy(gameObject);
     }
     
 }

And also sometimes its effects the enemy and when it does its effects only one enemy (the enemy's is very close to each other. I am sure the enemy is tagged as Enemy and the player as Player Can someone help me? thank you.