Information does not appear in DB

When you click submit, the information is not saved in DB

Query result: INSERT INTO usersTbL VALUES ('Maxim',258963417,'max',25,050,'9517427');

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;

namespace ORI
{
    public partial class sign_up : System.Web.UI.Page
    {
        public string st = "";
        public string msg = "5";
        public string sqlSelect = "";
        public string sqlInsert = "";
        protected void Page_Load(object sender, EventArgs e)
        {
            string fileName = "users2.mdf";
            string tableName = "usersTbL";

            if (Request.Form["submit"] != null)
            {
                string username = Request.Form["uName"];
                sqlSelect = "select uName from " + tableName;
                sqlSelect += " where uName = '" + username + "';";
                DataTable testTable = Helper.ExecuteDataTable(fileName, sqlSelect);

                if(Helper.IsExist(fileName, sqlSelect))
                {
                    msg = "user already exists";
                }
                else
                {
                    string id = Request.Form["id"];
                    string firstName = Request.Form["fName"];
                    string Nage = Request.Form["age"];
                    string prefix = Request.Form["prefix"];
                    string phone = Request.Form["phone"];
                    int Iage = int.Parse(Nage);

                    sqlInsert = "INSERT INTO " + tableName;
                    sqlInsert += " VALUES ('" + username + "','" + id + "','" + firstName + "'," + Iage + ",'" + prefix + "','" + phone + "');";

                    Helper.DoQuery(fileName, sqlInsert);

                }
            }
        }
    }
}