Ringtone continues playing when ListPreference value changes

Question

I have list of target values in ListPreference and I need to play sound when int i exceeds it (target value).

  String limit = sharedPreferences.getString("limit", getString(R.string.limitdef));
  switch (limit) {
            case "20":
                if (i >= 20) {
                    this.lets_dance();
                } else {
                    if (ringtone.isPlaying()) {
                        ringtone.stop();
                    }
                }
                break;
            case "30":
                if (i >= 30) {
                    this.lets_dance();
                } else {
                    if (ringtone.isPlaying()) {
                        ringtone.stop();
                    } 
                }
                break;
    }

void lets_dance:

  private void lets_dance() {
            if (!ringtone.isPlaying()) {
                ringtone.play();
            }
    }

And now my problem: for example when I start the app and target value is "20", but then I change my mind and cahnge it to "30", ringtone still starts playing when int i is >=20.