Unity does not change the scenes

In my Unity project I have these two scenes:

And I had this code to change the scene with a trigger:

void OnTriggerEnter2D(Collider2D other)
{

    //DETECTA TRIGGER PARA ENTRAR A CASA
    if(other.gameObject.name.Equals("casa")){
        Application.LoadLevel("casa");
    }

    //DETECTA TRIGGER SALIR DE CASA
    if(other.gameObject.name.Equals("salirDeCasa")){
        Application.LoadLevel("escenalibre");
    }
}

With this code worked perfectly, but the next day I opened the project and did not change the scenes and looking for Google I found this another way to do it:

void OnTriggerEnter2D(Collider2D other)
{

    //DETECTA TRIGGER PARA ENTRAR A CASA
    if(other.gameObject.name.Equals("casa")){
        SceneManager.LoadScene("casa",LoadSceneMode.Single);
    }

    //DETECTA TRIGGER SALIR DE CASA
    if(other.gameObject.name.Equals("salirDeCasa")){
        SceneManager.LoadScene("escenalibre",LoadSceneMode.Single);
    }
}

And adding the using UnityEngine.SceneManagement; .

Well, it does not work either ... But if I decide to change by the scene in which I am at that moment, if it changes by itself, it is as if being in a scene does not detect the others ...

Does anyone know if this has a solution? Or if I made a mistake in the code?