C# Serialization is working fine in Unity but not on Android

I'm aware, that there are multiple Questions about a similar topic out there already but still wasn't able to find a solution. I keep having the same problem, as already mentioned in the title I try saving data on android and in Unity everything is working as expected but as soon as i try on a real device it isn't saving anything (I tried 4 different devices). So today I tried again and even copied the code from an official tutorial (https://unity3d.com/learn/tutorials/modules/beginner/live-training-archive/persistence-data-saving-loading) but I stil couldn't get it working. Here is my Script:

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 using System.IO;
 using System.Runtime.Serialization.Formatters.Binary;
 using System;

 public class ScoreControll : MonoBehaviour {

 public int Score = 0;
 
 // Use this for initialization
 void Start () {
     
 }
 
 // Update is called once per frame
 void Update () {
     GameObject.Find("Score").GetComponent<Text>().text = "Score: " + Score;
 }
 void OnDisable()
 {
     Save();
 }
 void OnEnable()
 {
     Load();
 }
 public void Save()
 {
     BinaryFormatter bf = new BinaryFormatter();
     FileStream file = File.Create(Application.persistentDataPath + "/score.dat");

     ScoreData data = new ScoreData();
     data.Score = Score;

     bf.Serialize(file, data);
     file.Close();
 }
 
 public void Load()
 {
     if (File.Exists(Application.persistentDataPath + "/score.dat"))
     {
         BinaryFormatter bf = new BinaryFormatter();
         FileStream file = File.Open((Application.persistentDataPath + "/score.dat"),FileMode.Open);
         ScoreData data =(ScoreData) bf.Deserialize(file);
         file.Close();
         Score = data.Score;

     }
 }
 }
 [Serializable]
 class ScoreData
 {
     public int Score;
 }

I really hope for an easy answer.

Thanks in advance,

Pit Hüne

P.S. Im using Unity version 5.3.0f4 but I had the same issue in former versions aswell.