Problems with proxy c#

Very long ago I decided to write software for creating botnets in social networks. It all started with Instagram, but there I was soon banned on the IP, and I somehow podugas. After a while, I decided to rewrite the project under vk. And so, I have an authorization method. Tk I'm from Ukraine, I simply can't test authorization without a proxy(and access to many clients at the same time from one IP is not the best idea), probably there are shortcomings in it, but this is not about that now. I don't know why, but with proxies, I just don't get html. I use fresh, stogo http proxies. Here is the code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net.Http;
using Newtonsoft.Json;
using HtmlAgilityPack;
using System.Net;
using System.IO;
using System.Text.RegularExpressions;

namespace vkbot
{
    class VK : IDisposable
    {
        const string USER_AGENT =
            "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_3) " +
            "AppleWebKit/537.36 (KHTML, like Gecko) " +
            "Chrome/45.0.2414.0 Safari/537.36";

        HttpClientHandler m_handler;
        HttpClient m_client;

        public VK()
        {
            m_handler = new HttpClientHandler();
            m_client = new HttpClient(m_handler);
            m_client.BaseAddress = new Uri("https://vk.com/");
            m_client.DefaultRequestHeaders.UserAgent.ParseAdd(USER_AGENT);
            m_handler.UseProxy = true;
            m_handler.Proxy = new WebProxy("89.175.129.145:55653");
        }
        public void Dispose()
        {
            m_client.Dispose();
            m_handler.Dispose();
        }
        async void GetCookie()
        {
            await m_client.GetAsync("/login/");
            //var cookies = m_handler.CookieContainer.GetCookies(m_client.BaseAddress);
        }
        public async Task<string> LoginAsync(string username, string password)
        {
            HtmlDocument document = new HtmlDocument();
            document.LoadHtml(await m_client.GetAsync("/login").Result.Content.ReadAsStringAsync());
            string ip_h = Convert.ToString(document.DocumentNode.SelectSingleNode("/html/body/div[13]").InnerHtml);
            var cookies = m_handler.CookieContainer.GetCookies(m_client.BaseAddress);
            HttpRequestMessage message = new HttpRequestMessage(HttpMethod.Post, "/login/");
            message.Headers.Host = "login.vk.com";
            message.Headers.Referrer = m_client.BaseAddress;
            Dictionary<string, string> fields = new Dictionary<string, string>()
            {
                {"_origin", Convert.ToString(m_client.BaseAddress)},
                {"act","login" },
                {"email",username},
                {"pass",password },
                {"role","al_frame" }
            };
            var responce = await m_client.SendAsync(message);
            return responce.ToString();
        }

    }
}

The proxy initialized in the constructor, this is a temporary measure if anything.

PS now I ask you to help with the proxy, but if you have something to say about the rest of the code - write. I would be grateful.