var proxy = new WebProxy
{
    Address = new Uri("http://24.51.32.59:8080"),
    UseDefaultCredentials = false,
    BypassProxyOnLocal = false,
};

var handler = new HttpClientHandler
{
    Proxy = proxy
};

HttpClient client = new HttpClient(handler);
var response = await client.GetStringAsync("https://api.ipify.org/?format=text");
Console.Write(response);