Block Incoming calls in android without single ring

import java.lang.reflect.Method;

import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.media.AudioManager;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.telephony.PhoneStateListener;
import android.telephony.TelephonyManager;
import android.widget.Toast;

import com.android.internal.telephony.ITelephony;

public class PhoneCallStateListener extends PhoneStateListener {	
	
	private Context context;
	public PhoneCallStateListener(Context context){
		this.context = context;
	}

	
	@Override
	public void onCallStateChanged(int state, String incomingNumber) {	
	SharedPreferences prefs=PreferenceManager.getDefaultSharedPreferences(context);
	  
	switch (state) {
		
		case TelephonyManager.CALL_STATE_RINGING:		
			
		  String block_number = prefs.getString("block_number", null);
				AudioManager audioManager = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);	
				//Turn ON the mute
		audioManager.setStreamMute(AudioManager.STREAM_RING, true);					
				TelephonyManager telephonyManager = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
		try {
		Toast.makeText(context, "in"+block_number, Toast.LENGTH_LONG).show();
		Class clazz = Class.forName(telephonyManager.getClass().getName());
		Method method = clazz.getDeclaredMethod("getITelephony");
		method.setAccessible(true);
		ITelephony telephonyService = (ITelephony) method.invoke(telephonyManager);		
		//Checking incoming call number
		System.out.println("Call "+block_number);
		if (incomingNumber.equalsIgnoreCase("+91"+block_number)) {
		//telephonyService.silenceRinger();//Security exception problem
		 telephonyService = (ITelephony) method.invoke(telephonyManager);
		 telephonyService.silenceRinger();
		System.out.println(" in  "+block_number);
		telephonyService.endCall();
		}
		} catch (Exception e) {
		Toast.makeText(context, e.toString(), Toast.LENGTH_LONG).show();
		}
			//Turn OFF the mute		
		audioManager.setStreamMute(AudioManager.STREAM_RING, false);
		break;
		case PhoneStateListener.LISTEN_CALL_STATE:
		}
		super.onCallStateChanged(state, incomingNumber);
	}
}