Problems in the JsonConvert.SerializeObject and StringContent

I'm developing a Xamarin Forms application that will persist data via web service (PHP - MySQL), but I'm having trouble sending data via POST

I have the event below and the same as the message of Cadastrado com sucesso! , but when I check the database the information is empty.

Button event event code

private async void cadastroButton_Clicked(object sender, EventArgs e)
{
    if (string.IsNullOrEmpty(nomeEntry.Text))
    {
        await DisplayAlert("Erro", "Campo nome obrigatório!", "Ok");
        nomeEntry.Focus();
        return;
    }
    if (string.IsNullOrEmpty(celularEntry.Text))
    {
        await DisplayAlert("Erro", "Campo celular obrigatório!", "Ok");
        celularEntry.Focus();
        return;
    }

    waitActivityIndicator.IsVisible = true;
    waitActivityIndicator.IsRunning = true;

    var ramal = new DeviceRamal
    {   
        ram_nome = nomeEntry.Text,            
        ram_celular = celularEntry.Text,
    };

    var jsonRequest = JsonConvert.SerializeObject(ramal);
    var content = new StringContent(jsonRequest, Encoding.UTF8, "text/json");

    string result;

    try
    {
        HttpClient client = new HttpClient();
        client.BaseAddress = new Uri("http://meusite.com.br");
        string url = string.Format("/contato/insert.php");
        var response = await client.PostAsync(url, content);
        result = response.Content.ReadAsStringAsync().Result;
    }
    catch (Exception)
    {
        await DisplayAlert("Erro", "Sem conexão no momento!", "Ok");
        return;
    }


    waitActivityIndicator.IsVisible = false;
    waitActivityIndicator.IsRunning = false;
    await DisplayAlert("Sucesso", "Cadastrado com sucesso!", "Ok");
}

If you do so Do not send the parameters

string url = string.Format("/contato/insert.php");
var response = await client.PostAsync(url, content);

If you do this Send the parameters

string url = string.Format("/contato/index.php?email={0}&password={1}", userEntry.Text, passwordEntry.Text);
var response = await client.GetAsync(url);

I got the try catch and the response returns the following:

  

{StatusCode: 200, ReasonPhrase: 'OK', Version: 1.1, Content:> System.Net.Http.StreamContent, Headers:   {   Date: Thu, 04 Aug 2016 00:59:45 GMT   Server: Apache   X-Powered-By: PHP / 5.4.42   Connection: close   Transfer-Encoding: chunked   Content-Type: text / html   }}

Note with PostAsync does not work, with GetAsync works, client.PostAsync("http://site.com.br/appramal/f/insertRamal.php?ram_celular={0}" ...

And I moved in the code and it still does not work.

    private async void cadastroRamalButton_Clicked(object sender, EventArgs e)
    {
        if (unidadePicker.SelectedIndex == -1)
        {
            await DisplayAlert("Erro", "Selecione a unidade", "Ok");
            unidadePicker.Focus();
            return;
        }
        if (string.IsNullOrEmpty(nomeEntry.Text))
        {
            await DisplayAlert("Erro", "Campo nome obrigatório!", "Ok");
            nomeEntry.Focus();
            return;
        }
        if (string.IsNullOrEmpty(ramalEntry.Text))
        {
            await DisplayAlert("Erro", "Campo nome obrigatório!", "Ok");
            ramalEntry.Focus();
            return;
        }
        if (string.IsNullOrEmpty(ramalVirtualEntry.Text))
        {
            await DisplayAlert("Erro", "Campo ramal virtual obrigatório!", "Ok");
            ramalVirtualEntry.Focus();
            return;
        }
        if (string.IsNullOrEmpty(celularEntry.Text))
        {
            await DisplayAlert("Erro", "Campo celular obrigatório!", "Ok");
            celularEntry.Focus();
            return;
        }
        if (setorPicker.SelectedIndex == -1)
        {
            await DisplayAlert("Erro", "Selecione o setor", "Ok");
            setorPicker.Focus();
            return;
        }
        if (string.IsNullOrEmpty(emailEntry.Text))
        {
            await DisplayAlert("Erro", "Campo email obrigatório!", "Ok");
            emailEntry.Focus();
            return;
        }
        if (string.IsNullOrEmpty(skypeEntry.Text))
        {
            await DisplayAlert("Erro", "Campo skype obrigatório!", "Ok");
            skypeEntry.Focus();
            return;
        }

        waitActivityIndicator.IsVisible = true;
        waitActivityIndicator.IsRunning = true;

        DeviceRamal ramal = new DeviceRamal();
        ramal.ram_celular = celularEntry.Text;
        ramal.ram_email = emailEntry.Text;
        ramal.ram_nome = nomeEntry.Text;
        ramal.ram_ramal = ramalEntry.Text;
        ramal.ram_ramalvirtual = ramalVirtualEntry.Text;
        ramal.ram_skype = skypeEntry.Text;
        ramal.set_codigo = this.setorList[setorPicker.SelectedIndex].set_codigo;
        ramal.uni_codigo = this.unidadeList[unidadePicker.SelectedIndex].uni_codigo;

        string result;

        HttpClient client = new HttpClient();

        var response = client.PostAsync("http://site.com.br/appramal/f/insertRamal.php",
            new StringContent(JsonConvert.SerializeObject(ramal).ToString(),
            Encoding.UTF8, "application/json")).Result;

        if (response.IsSuccessStatusCode)
        {
            dynamic content = JsonConvert.DeserializeObject(response.Content.ReadAsStringAsync().Result);

            await DisplayAlert("Sucesso", "Ramal cadastrado com sucesso!", "Ok");
            waitActivityIndicator.IsVisible = false;
            waitActivityIndicator.IsRunning = false;
        }

    }