Consume webService C # amsx on android volley

I created a webservice in C # that returns me a string in the JSON pattern, I'm trying to consume this webservice with the volley but the same one returns me null, depending on the variation of the url it returns everything to me as if it were? wsdl but not the function I want, it's like missing the click on invoke.

My url looks like this: url=" link ";

I've tried variations url=" link among others

My code looks like this:

Thanks to everyone

package com.example.voleytest.voleytest;

import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;
import android.widget.Toast;

import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;

import java.util.HashMap;
import java.util.Map;


public class MainActivity extends ActionBarActivity {


       private RequestQueue queue;
    private String url;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        url = "http://10.0.2.2/webServiceFlux/WS/SewrvicoBase.asmx?op=buscar";

        queue = Volley.newRequestQueue(MainActivity.this);

        callByJsonObjectRequest(null);
    }


    public void callByJsonObjectRequest(View view){

        // Request a string response from the provided URL.
        StringRequest stringRequest = new StringRequest(Request.Method.POST, url,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        // Display the first 500 characters of the response string.

                        Toast.makeText(MainActivity.this, "Response is: " + response.substring(0, 500), Toast.LENGTH_LONG).show();
                    }
                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Toast.makeText(MainActivity.this, "Error: "+error.getMessage(), Toast.LENGTH_LONG).show();
            }




        }

        ) };
// Add the request to the RequestQueue.
        queue.add(stringRequest);


    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}