Here is a self-sufficient (no WCF, no WSDL, ...) utility class that will check the VAT number and get information on the company (name and address). It will return null if the VAT number is invalid or if any error occurred.

Update 2022/10/17 : I have added namespace handling to parse the response as it seems the EU web service was modified. If you need the old version, just look at the history

// sample calling code
Console.WriteLine(EuropeanVatInformation.Get("FR89831948815"));

...

public class EuropeanVatInformation
{
    private EuropeanVatInformation() { }

    public string CountryCode { get; private set; }
    public string VatNumber { get; private set; }
    public string Address { get; private set; }
    public string Name { get; private set; }
    public override string ToString() => CountryCode + " " + VatNumber + ": " + Name + ", " + Address.Replace("\n", ", ");

    public static EuropeanVatInformation Get(string countryCodeAndVatNumber)
    {
        if (countryCodeAndVatNumber == null)
            throw new ArgumentNullException(nameof(countryCodeAndVatNumber));

        if (countryCodeAndVatNumber.Length < 3)
            return null;

        return Get(countryCodeAndVatNumber.Substring(0, 2), countryCodeAndVatNumber.Substring(2));
    }

    public static EuropeanVatInformation Get(string countryCode, string vatNumber)
    {
        if (countryCode == null)
            throw new ArgumentNullException(nameof(countryCode));

        if (vatNumber == null)
            throw new ArgumentNullException(nameof(vatNumber));

        countryCode = countryCode.Trim();
        vatNumber = vatNumber.Trim().Replace(" ", string.Empty);

        const string ns = "urn:ec.europa.eu:taxud:vies:services:checkVat:types";
        const string url = "http://ec.europa.eu/taxation_customs/vies/services/checkVatService";
        const string xml = @"<s:Envelope xmlns:s='http://schemas.xmlsoap.org/soap/envelope/'><s:Body><checkVat xmlns='" + ns + "'><countryCode>{0}</countryCode><vatNumber>{1}</vatNumber></checkVat></s:Body></s:Envelope>";

        try
        {
            using (var client = new WebClient())
            {
                var doc = new XmlDocument();
                doc.LoadXml(client.UploadString(url, string.Format(xml, countryCode, vatNumber)));
                var response = doc.SelectSingleNode("//*[local-name()='checkVatResponse']") as XmlElement;
                if (response == null || response["valid", ns]?.InnerText != "true")
                    return null;

                var info = new EuropeanVatInformation
                {
                    CountryCode = response["countryCode", ns].InnerText,
                    VatNumber = response["vatNumber", ns].InnerText,
                    Name = response["name", ns]?.InnerText,
                    Address = response["address", ns]?.InnerText
                };
                return info;
            }
        }
        catch
        {
            return null;
        }
    }
}