Не получается получить ответ на GET-запрос

var req = (HttpWebRequest)WebRequest.Create("https://tele2.ru/api/subscribers/номер_телефона/rests");
req.CookieContainer = new CookieContainer();
req.CookieContainer.Add(new Uri("https://tele2.ru/?pageParams=authorized=true"), cook);
req.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8";
req.Headers.Add("Accept-Encoding", "gzip, deflate, br");
req.Headers.Add("Accept-Language", "ru-RU,ru;q=0.8,en-US;q=0.5,en;q=0.3");
req.KeepAlive = true;
req.Headers.Add("DNT", "1");
req.Host = "tele2.ru";
req.UserAgent = "Mozilla/5.0 (Windows NT 6.1; rv:62.0) Gecko/20100101 Firefox/62.0";
req.AllowAutoRedirect = false;

using (var request = new HttpRequest())
{
    request.Cookies = cookies;
    foreach (var c in cookies)
    {
        if (cookies.ContainsKey(c.Key) && cookies.ContainsValue(c.Value)) continue;
        cookies.Add(c.Key, c.Value);
 
        request.Cookies = new CookieDictionary()
        {
            {c.Key, c.Value},
        };
    }
    request.AddHeader("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8");
    request.UserAgent = "Mozilla/5.0 (Windows NT 6.1; rv:62.0) Gecko/20100101 Firefox/62.0";
    HttpResponse response = request.Get("https://tele2.ru/api/subscribers/номер_телефона/rests");
    string content = response.ToString();
 
    textBox1.Text = $"{content}\r\n\r\n";
 
    foreach (var c in cookies)
    {
        textBox1.Text += $"{c.Key}: {c.Value}";
    }
}

{"meta":{"status":"ERROR","message":"sso session key should not be empty"},"data":null}

private static CookieCollection cook;
 
try
{
    var request = (HttpWebRequest)WebRequest.Create("https://tele2.ru/api/subscribers/номер_телефона/rests");
    request.CookieContainer = new CookieContainer();
    request.CookieContainer.Add(new Uri("https://login.tele2.ru/ssotele2/wap/auth"), cook);
    request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8";
    request.UserAgent = "Mozilla/5.0 (Windows NT 6.3; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36";
    request.ContentType = "application/json;charset=utf-8";
    request.KeepAlive = true;
    request.AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate;
    request.Headers.Add("DNT", "1");
    request.Method = "GET";
 
    using (var response = (HttpWebResponse)await request.GetResponseAsync())
    {
        using (var read = new StreamReader(response.GetResponseStream()))
        {
            var result = await read.ReadToEndAsync();
        }
    }
}
catch (WebException w)
{
    using (WebResponse response = w.Response)
    {
        HttpWebResponse httpResponse = (HttpWebResponse)response;
        this.Text = $"Error code: {httpResponse.StatusCode}";
        using (Stream data = response.GetResponseStream())
        using (var reader = new StreamReader(data))
        {
            string text = reader.ReadToEnd();
            textBox1.Text = text;
        }
    }
}

var request = (HttpWebRequest)WebRequest.Create("https://login.tele2.ru/ssotele2/wap/auth");
request.CookieContainer = new CookieContainer();
request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8";
request.UserAgent = "Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:62.0) Gecko/20100101 Firefox/62.0";
 
using (var response = (HttpWebResponse)await request.GetResponseAsync())
{
    cook = response.Cookies;
    using (var read = new StreamReader(response.GetResponseStream()))
    {
        // другой код..
    }
}