How Do I Get Credit Card Type By Giving The Credit Card Number

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ASP.NET

I am trying to get the credit card type when we give a credit card number i.e. when user gives a credit card number in a text box that input has to be taken validated using luhn check and get the type of card as AMEX, VISA etc.
I have gone through some examples in codeproject and tried to implement but i am unable to take the input into class created for different card types, i used regex and the code in c# is as below:

 C# 
protected void TextBox1_TextChanged(object sender, EventArgs e)
    {
        int luhnCheckdigit = 0;

         string cardNumber = TextBox1.Text.ToString();
        luhnCheckdigit = checkSum(TextBox1.Text.ToString());
        string TYPE = cardType(TextBox1.Text.ToString());
    }
public enum cardType
    {
        unknown = 0,
        MasterCard = 1,
        VISA = 2,
        AMEX = 3
    }
public class CardtypeInfo
    {
        public  CardtypeInfo(string regEx, int length, cardType type)
        {

            RegEx = regEx;
            Length = length;
            TYpe = type;
        }
        public string RegEx { get; set; }
        public int Length { get; set; }
        public cardType TYpe { get; set; }
    }
private static CardtypeInfo[] _CardTypeInfo = 
    {
        new CardtypeInfo("^(51|52|53|54|55)", 16, cardType.MasterCard),
        new CardtypeInfo("^(4)", 16,cardType.VISA),
        new CardtypeInfo("^(4)",13, cardType.VISA),
        new CardtypeInfo("^(34|37)",15,cardType.AMEX),
    };
    public cardType GetcardType(string cardNumber)
    {
        
        foreach (CardtypeInfo info in _CardTypeInfo)
        {
            if (cardNumber.Length == info.Length && Regex.IsMatch(cardNumber, info.RegEx))

                return info.TYpe;

        }
        return cardType.unknown;
    }

please help me to get the input into the class cardtype and display the type of card when the text change event occured.