For anyone that has this problem, try verifying that you access the correct file, so the path that you the streamreader is a correct one. The best way, for me, is
StreamReader streamReader = new StreamReader(Application.persistentDataPath + “/” + “filename”);
This if for c#. the string filename should be exactly the name of the file you need to access. Application.persistanceDataPath is the path where your application saves a xml file if you create one on your own. To verify it’s value just write print(Application.persistentDataPath); and it will write in the console were to go if you want to edit that xml file manually