Why does the next scene not loading?

I have two scripts.One attached to the main GameObject named player(which is the actual player) and one that handles the scene loading which is attached to an empty GameObject.

So…the problem is focused on the CompleteLevel() method and OnTriggerEnter() method.I am mentioning that I put a “Goal” tag to the Goal game object .When I collide with the Goal GameObject nothing happens.I have two levels and I want to load the next one when I collide with the Goal GameObject.The leavels are loaded in the Build settings.
I don’t know what I am missing,and why the script does not work…

Please help.If you have a solution write it down.Thanx.

Here are the scripts :

The one attached to the “player” GameObject:

public class PlayerMouvement : MonoBehaviour {

public float moveSpeed ; 
public Vector3 spawn;
public GameObject deathParticles;
public float fallDistance;
private Vector3 input;
private Rigidbody rb;
private float maxSpeed = 5;

// Use this for initialization
void Start () 
{
	rb = GetComponent<Rigidbody> ();
	spawn = transform.position;
}

// Update is called once per frame
void Update () 
{
	
	//Takes mouvment input from the player keys.
	input = new Vector3 (Input.GetAxisRaw ("Vertical"), 0, Input.GetAxisRaw ("Horizontal"));
	//This ensurs that the acceleration wil be snappy,and dramatic,not progresive.
	if (rb.velocity.magnitude < maxSpeed) 
	{
		rb.velocity = new Vector3 (Input.GetAxisRaw ("Vertical"), 0, Input.GetAxisRaw ("Horizontal")) * maxSpeed;
	}
	//This makes shore that the player will mouve based on input.
	//print (input);
	rb.AddForce (input * moveSpeed);  
	//if the player falls of the map the Death() function will be called.
	if (transform.position.y < fallDistance) 
	{
		Death ();
	}
}
//If the player hits an enamy the Death() function is called.
void OnCollisionEnter(Collision other){
	if (other.transform.tag == "Enamy") 
	{
		Death ();
	}
}
//Loads the next Level when the player collides with the "Goal".
void OnTriggerEnter(Collider other)
{
	if (other.transform.tag == "Goal") 
	{
		GameManager.CompleteLevel();
	}
}

//This makes the player die,playe death particles and respown at the starting point.
void Death()
{
	print ("The player has died");
	Instantiate (deathParticles,transform.position, Quaternion.identity);
	transform.position = spawn;
}

}

And I have this one named GameManager attached to the empty GameObject:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;

public class GameManager : MonoBehaviour {

public static int currentScore;
public static int highScore;
public static int currentLevel = 0;
public static int unlockedLevel;

public static void CompleteLevel()
{
	currentLevel +=1;
	SceneManager.LoadScene (currentLevel +1);
}

}

I am a begainner,can you corect my code and post it here? I am really bad at programming,tryng to learn.