Ennemy don't lose life [C#]

Hello Everybody ! I'm creating a little game where ennemies goes to a castle and you are a tower who defend the castle. But I have a problem... When my ennemy is touching the castle, the castle lose 1 life but when my bullet touch the ennemy, he don't lose life... I created a empty child for the collider of my ennemy, and one for my bullet but it doesn't work.... This is my ennemy script

using UnityEngine; using System.Collections;

public class Ennemy : MonoBehaviour { private NavMeshAgent agent; public static int lvl = 1; public static double Damage; public static double Vies = 10;

 void Start () {
     lvl = 1;
     agent = GetComponent<NavMeshAgent>();     //déplacement
     //NavMeshPath chemin = new NavMeshPath();
     agent.destination = GameObject.Find ("Castle").transform.position;  //sa destination est la postition de "castle"
 }
 

 void Update () {
     Damage = GameManager.Damage;

     Vies = 10 + (lvl * 3);
     //////////////////////////////////////////////////////////// VIES PAR LEVEL
     if (GameManager.score >= 250){
         lvl = 2;
     }
     if (GameManager.score >= 500){
         lvl = 3;
     }
     if (GameManager.score >= 750){
         lvl = 4;
     }
     if (GameManager.score >= 1000){
         lvl = 5;
     }
     if (GameManager.score >= 2250){
         lvl = 6;
     }
     if (GameManager.score >= 2500){
         lvl = 7;
     }
     if (GameManager.score >= 2750){
         lvl = 8;
     }
     if (GameManager.score >= 2000){
         lvl = 9;
     }
     if (GameManager.score >= 2250){
         lvl = 10;
     }
     if (GameManager.score >= 2500){
         lvl = 11;
     }
     if (GameManager.score >= 2750){
         lvl = 12;
     }
     if (GameManager.score >= 3000){
         lvl = 13;
     }
     if (GameManager.score >= 3250){
         lvl = 14;
     }
     if (GameManager.score >= 3500){
         lvl = 15;
     }
     if (GameManager.score >= 3750){
         lvl = 16;
     }
     if (GameManager.score >= 4000){
         lvl = 17;
     }
     if (GameManager.score >= 4250){
         lvl = 18;
     }
     if (GameManager.score >= 4500){
         lvl = 19;
     }
     if (GameManager.score >= 4750){
         lvl = 20;
     }
     if (GameManager.score >= 5000){
         lvl = 21;
     }
     if (GameManager.score >= 5250){
         lvl = 22;
     }
     if (GameManager.score >= 5500){
         lvl = 23;
     }
     if (GameManager.score >= 5750){
         lvl = 24;
     }
     if (GameManager.score >= 5000){
         lvl = 25;
     }
     if (GameManager.score >= 5250){
         lvl = 26;
     }
     if (GameManager.score >= 5500){
         lvl = 27;
     }
     if (GameManager.score >= 5750){
         lvl = 28;
     }
             
     //////////////////////////////////////////////////////////// VIES PAR LEVEL


     if (Vies <= 0) {
         Destroy(this.gameObject);
         GameManager.argent += 1;
         GameManager.score += 5;
     }
 }

 void OnTriggerEnter (Collider col){
     if (col.gameObject.name == "Castle") {
         TextVie.vie--;
         Destroy (this.gameObject);
     } 
     if (col.gameObject.name == "Bullet(Clone)") {            
         Vies -= Damage;
         Destroy (col.gameObject);
     }
 }

}

Thank you very much, that reading my post, i hope some one can help me.... Bye, xyHeat