NullReferenceException error with dreamlo

Hello everyone. I hope you all are fine when reading this. I'm having some difficulties using dreamlo. When I attempt to upload the new highscore, it shows this error.

NullReferenceException: Object reference not set to an instance of an object Highscores.AddNewHighScore (System.String user, Int32 score) (at Assets/Codigo/Highscores.cs:19) Player.CargarInfo () (at Assets/Codigo/Player.cs:50) Player.Update () (at Assets/Codigo/Player.cs:44)

I've been struggling with this error for days. Can someone help me with this? Thanks a lot.

Highscores.cs

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Highscores : MonoBehaviour {
     const string privateCode = "ayd1m1W5uUqyihLPs5h3PQihlj5MvDeEGg9_NLJ02u-Q";
     const string publicCode = "58741e6eb6dd1500a4ca66df";
     const string webURL = "http://dreamlo.com/lb/";
 
     public HighScore[] highScoresList;
     static Highscores instance;
     DisplayHighScores highscoresDisplay;
 
     void Awake () {
         highscoresDisplay = GetComponent<DisplayHighScores> ();
     }
 
     public static void AddNewHighScore(string user, int score){
         instance.StartCoroutine (instance.UploadNewHighScore (user, score));
     }
 
     IEnumerator UploadNewHighScore (string user, int score){
         WWW www = new WWW (webURL + privateCode + "/add/" + WWW.EscapeURL(user) + "/" + score);
         yield return www;
 
         if (string.IsNullOrEmpty (www.error)) {
             print ("Upload OK");
             DownloadHighScores ();
         } else {
             print ("Error upload " + www.error);
         }
     }
 
     public void DownloadHighScores(){
         StartCoroutine ("DownloadHighScoresFromDatabase");
     }
 
     IEnumerator DownloadHighScoresFromDatabase (){
         WWW www = new WWW (webURL + publicCode + "/pipe");
         yield return www;
 
         if (string.IsNullOrEmpty (www.error)) {
             FormatHighScores (www.text);
             highscoresDisplay.OnHighScoresDownloaded (highScoresList);
         } else {
             print ("Error Download " + www.error);
         }
     }
 
     void FormatHighScores (string textStream){
         string[] entries = textStream.Split (new char[] { '\n' }, System.StringSplitOptions.RemoveEmptyEntries);
 
         highScoresList = new HighScore[entries.Length];
 
         for(int i = 0; i < entries.Length; i++){
             string[] entryInfo = entries [i].Split(new char[] {'|'});
             string user = entryInfo [0];
             int score = int.Parse(entryInfo [1]);
             highScoresList [i] = new HighScore (user, score);
             print (highScoresList [i].user + ": " + highScoresList [i].score);
         }
     }
 }
 
 public struct HighScore {
     public string user;
     public int score;
 
     public HighScore(string _user, int _score){
         user = _user;
         score = _score;
     }
 }

Player.cs

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Player : MonoBehaviour {
 
     private GameObject menu;
     public MainMenu mainMenu;
 
     private GameObject tiempo;
     public Timer puntos;
 
     public int health;
 
     public int score;
     public string user = "";
 
     // Use this for initialization
     void Awake () {
         health = 1;
     }
 
     void Start () {
         user = PlayerPrefs.GetString ("Nombre");
 
         tiempo = GameObject.Find ("Reloj");
         puntos = tiempo.GetComponent<Timer> ();
     }
     
     // Update is called once per frame
     public void OnTriggerEnter (Collider other) {
         if (other.gameObject.tag == "Enemy") {
             health = 0;
             Destroy (other.gameObject);
         }
     }
 
     public void Update (){
         score = puntos.reloj;
         Debug.Log (score);
 
         if (health <= 0) {
             CargarInfo ();
             Destroy (this.gameObject);
         }
     }
 
     public void CargarInfo (){
         Highscores.AddNewHighScore ("" + PlayerPrefs.GetString("Nombre"), score);
     }
 }