How to have UI Manager come up on collision?

Hello, I am creating a collision game and I want to bring the game menu when I'm done. Even though my code seems right, when the object collides the menu doesn't come up. I will award best answer using UnityEngine; using System.Collections;

 public class EnemyDestroyer : MonoBehaviour {
     public UIManager ui;
     // Use this for initialization
     void Start () {
         ui = GetComponent<UIManager> ();
 
 
     }
     
     // Update is called once per frame
     void Update () {
         
     }
 
     void OnCollisionEnter2D(Collision2D col){
         if (col.gameObject.tag == "EnemyCar") {
             Destroy (col.gameObject);
             ui.gameOverActivated();
 
         }
     }
 }