How to validate user for Signup using Stored Procedure in SQL Server

Hi,

I want make user sign-up form in my project. for that i was created one table as Customer, and stored procedure as Customer_Signup. refer the code below. am not able insert data in to the table using asp web-form, help me how to load signup data to sqlserver database.

/****************** Object: Table [dbo].[Customer]    Script 16-01-2017 **************/

CREATE TABLE [dbo].[Customer] 
(
[Cus_SKY] [BIGINT] IDENTITY(1,1) NOT NULL,
[Email] [NVARCHAR] (100) NOT NULL,
[Phone] [BIGINT] NOT NULL,
[Key] [NVARCHAR] (32) NOT NULL,
[DATE_Created] DATETIME NOT NULL,
[Last_Login] DATETIME NULL,
CONSTRAINT [PK_Customer] PRIMARY KEY CLUSTERED ([Cus_SKY] ASC) WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS=ON, ALLOW_PAGE_LOCKS=ON) ON [PRIMARY]
)
GO


/**************** OBJECT: PROCEDURE [dbo].[Customer_Signup]     Script 16-01-2017 *******************/

SET QUOTED_IDENTIFIER ON
GO

ALTER PROCEDURE [dbo].[Customer_Signup] 
	@Email [NVARCHAR] (100),
	@Phone [BIGINT],
	@Key [NVARCHAR] (32)
AS
BEGIN
	SET NOCOUNT ON;
	IF EXISTS(SELECT Cus_SKY FROM Customer WHERE Email = @Email)
	BEGIN
		RETURN -1  --Customer email exists already
	END
	IF EXISTS(SELECT Cus_SKY FROM Customer WHERE Phone = @Phone)
	BEGIN
		RETURN -2   -- Customer phone number alredy exists
	END
	ELSE
	BEGIN
		INSERT INTO [Customer]
				([Email],
				[Phone],
				[Key],
				[DATE_Created])
		VALUES (@Email,
				@Phone,
				@Key,
				GETDATE())
		--SELECT SCOPE_IDENTITY()  -- Identity of Cus_SKY Scope()
	END
END

GO

use Holidays
SELECT * FROM Customer

 here is the background code to execute the procedure, but it's inserted first time, there after not inserting, not showing error message also.

        int userId = 0;
        string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        
        using (SqlConnection con = new SqlConnection(constr))
        {
            using (SqlCommand cmd = new SqlCommand("Customer_Signup"))
            {
                using (SqlDataAdapter sda = new SqlDataAdapter())
                {
                    cmd.CommandType = CommandType.StoredProcedure;
                    cmd.Parameters.AddWithValue("@Email", txtEmail.Text.Trim());
                    cmd.Parameters.AddWithValue("@Phone", txtPhone.Text.Trim());
                    cmd.Parameters.AddWithValue("@Key", txtPassword.Text.Trim());
                    cmd.Connection = con;
                    con.Open();
                    userId = Convert.ToInt32(cmd.ExecuteScalar());
                    con.Close();
                }
            }
            string message = string.Empty;
            switch (userId)
            {
                case -1:
                    message = "Supplied email address has already been used \\nPlease choose a different email.";
                    break;
                case -2:
                    message = "Supplied Phone number has already been used.";
                    break;
                default:
                    message = "Registration successful. Activation email has been sent.";
                    //SendActivationEmail(userId);
                    break;
            }
            ClientScript.RegisterStartupScript(GetType(), "alert", "alert('" + message + "');", true);