Xamarin - SMPT OFFICE365: sending emails has stopped working for me

Question

I developed an application with xamarin, a few months ago, to send emails, here a piece of my code:

public Email(string To, string CC, string Subject, string Body)
    Server = new SmtpClient
    {
        Host = "smtp.office365.com",
        Port = 587,
        EnableSsl = true,
        UseDefaultCredentials = false,
        DeliveryMethod = SmtpDeliveryMethod.Network,
        Credentials = new NetworkCredential("no-reply@contoso.com", "pass")
    };

    ServicePointManager.ServerCertificateValidationCallback = delegate (object s, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) { return true; };

    From = "no-reply@contoso.com";
    this.To = To;
    this.CC = CC;
    this.Subject = Subject;
    this.Body = Body;
}

public void SendEmail()
{
    try
    {
        var correo = new MailMessage();
        correo.From = new MailAddress(From);
        correo.To.Add(To);

        if (!string.IsNullOrEmpty(CC))
            correo.CC.Add(CC);

        correo.Subject = Subject;
        correo.IsBodyHtml = true;
        correo.Body = Body;

        //Enable suport TLS1.2
        ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
        Server.EnableSsl = true;

        Server.SendCompleted += (s, e) => Server.Dispose();
        Server.Send(correo);
    }
    catch (Exception ex)
    {
        Device.BeginInvokeOnMainThread(async () => { await Application.Current.MainPage.DisplayAlert("Error al enviar correu", $"Message: {ex.Message}\n\n Inner Exception: {ex.StackTrace}", "Ok"); });
    }
}

This app has worked correctly so far. Now I'm getting and error when I'm trying to send an email.

Here a trace from the error:

"System.Net.Mail.SmtpException: Message could not be sent. ---> System.IO.IOException: Authentication failed because the remote party has closed the transport stream.\n at Mono.Net.Security.AsyncProtocolRequest.ProcessOperation......."

I was looking through several forums to get with the response, but I was unable to find it. A lot of answer were related with use TLS12, but I'm currently using it.

Any help?

Thanks in advance