Score counter not working properly.

Heya, I am new to Unity and c# ... I am just making a simple vertical shooter and am now up to keeping score! I just want to score 1 point each time an enemy is destroyed (all it takes is one shot from the bullet). Now at the moment, what my score counter is doing is scoring a point each time you hit the enemy, however if you miss the enemy, say 3 times in a row, the score will tally up for when you next hit the enemy.. So you could be on 1 point, miss three times, then hit an enemy and your score will go from 1 to 4 . I tried changing the score codes from the EnemyScript and putting it instead in the BulletScript, but no change. I think it's something simple I am missing but I am not sure what it is! Any help would be appreciated.. Here is my bullet script as it stands currently:

using UnityEngine; using UnityEngine.UI; using System.Collections;

public class BulletScript : MonoBehaviour {

 public float BulletSpeed = 5f;
 public PlayerController playerController;
 public int Count;
 public Text CountText;


 void Update () { 
     transform.Translate (Vector3.up * BulletSpeed * Time.deltaTime);

 }
 void OnBecameInvisible () { 
     this.gameObject.SetActive (false);
 }

 void OnTriggerEnter2D(Collider2D other)
 {

     if (other.gameObject.tag == "Enemy")
         gameObject.SetActive (false);

     playerController.CountText.text = playerController.Count.ToString();


 }

 void Start() { 
     playerController = GameObject.FindGameObjectWithTag("Player").GetComponent<PlayerController>();

 }

}

Thank you!