Android : Can't send data to Arduino Due from Android via Bluetooth

I have written an Android app that's supposed to send data to Arduino Due via Bluetooth Module (ZS-040). Bluetooth connection is fine. However, Arduino doesn't seem to receive any data from Android. When I send data to Arduino through the Serial Monitor though, it works. I've looked into many stackoverflow questions and other guides online but can't seem to figure out what's wrong.

Here's some code:

Thread for connecting the two devices:

private class ConnectThread extends Thread {
    private BluetoothDevice mmDevice;
    private final UUID MY_UUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
    //uuid for Arduino bluetooth module

    public ConnectThread(BluetoothDevice device) {
        BluetoothSocket tmp = null;
        mmDevice = device;

        try {
            tmp = mmDevice.createRfcommSocketToServiceRecord(MY_UUID);
        } catch (IOException e) { };
        socket = tmp;
    }

    public void run() {
        mBluetoothAdapter.cancelDiscovery();
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                findBtn.setText("Search for devices");
            }
        });

        try {
            socket.connect();
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    Toast.makeText(getBaseContext(), "Success", Toast.LENGTH_SHORT).show();
                }
            });
        } catch (IOException connectionException) {
            try {
                socket.close();
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        Toast.makeText(getBaseContext(), "An error has occured. Please try again.",
                                Toast.LENGTH_SHORT).show();
                    }
                });
            } catch (IOException closeException) { }
            return;
        }
    }
}

Code for sending data to Arduino; function is called when a button is pressed.

public void sendData(View view) {
    // write to OutputStream
    OutputStream mmOutputStream = null;
    try {
        mmOutputStream = socket.getOutputStream();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        System.out.println(e.getMessage());
        e.printStackTrace();
    }
//  String message = "0";
//  byte[] msgBuffer = message.getBytes();

    try {
        mmOutputStream.write('0');
    } catch (IOException e) {
        // TODO Auto-generated catch block
        System.out.println(e.getMessage());
        e.printStackTrace();
    }   
}

Arduino code (directly copied from here):

char incomingByte;  // incoming data
int  LED = 12;      // LED pin

void setup() {
  Serial.begin(9600); // initialization
  pinMode(LED, OUTPUT);
  Serial.println("Press 1 to LED ON or 0 to LED OFF...");
}

void loop() {
  if (Serial.available() > 0) {  // if the data came
    incomingByte = Serial.read(); // read byte
    if(incomingByte == '0') {
       digitalWrite(LED, LOW);  // if 1, switch LED Off
       Serial.println("LED OFF. Press 1 to LED ON!");  // print message
    }
    if(incomingByte == '1') {
       digitalWrite(LED, HIGH); // if 0, switch LED on
       Serial.println("LED ON. Press 0 to LED OFF!");
    }
  }
}

EDIT: Because it's a DUE with which I'm working, I can't use SoftwareSerial library. :(