[Solved] ASP.Net: String concatenation not working in C#

Dear Sir,

While i have send sms it's not sending due to mobile number not fetch from GridView.

Please help me sir.

namespace OCMS
{
    public partial class admin : System.Web.UI.Page
    {
        SqlConnection con = new SqlConnection(@"Data Source=10.1.246.4;Initial Catalog=OCMS;User ID=dba_ntpc_meja_intranet;Password=alpha$890;Connect Timeout=30;Encrypt=False;TrustServerCertificate=False;ApplicationIntent=ReadWrite;MultiSubnetFailover=False");
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                refreshdata();
            }
        }
        public void refreshdata()
        {
            con.Open();
            //SqlCommand cmd = new SqlCommand("select * from comp_box where closing_date IS NULL ORDER BY COMP_ID DESC ", con);
            SqlCommand cmd = new SqlCommand("select * from comp_box,emp where closing_date IS NULL and comp_box.emp_id=emp.emp_id order by comp_lodge_date desc", con);
            SqlDataAdapter sda = new SqlDataAdapter(cmd);
            DataTable dt = new DataTable();
            sda.Fill(dt);
            con.Close();
            GridView1.DataSource = dt;
            GridView1.DataBind();
        }
        protected void Closed(object sender, EventArgs e)
        {

            GridViewRow row = (sender as Button).NamingContainer as GridViewRow;
            int COMP_ID = Convert.ToInt32(GridView1.DataKeys[Convert.ToInt32((sender as Button).CommandArgument)].Values[0]);
            string STATUS_ID = "02";
            string remark = (row.FindControl("TextBox5") as TextBox).Text;
            string CLOSING_DATE = DateTime.Now.ToString();

            string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
            using (SqlConnection con = new SqlConnection(constr))
            {
                using (SqlCommand cmd = new SqlCommand("UPDATE comp_box SET STATUS_ID = @STATUS_ID, REMARKS = @REMARKS,CLOSING_DATE = @CLOSING_DATE WHERE COMP_ID = @COMP_ID"))
                {
                    cmd.Parameters.AddWithValue("@COMP_ID", COMP_ID);
                    cmd.Parameters.AddWithValue("@STATUS_ID", STATUS_ID);
                    cmd.Parameters.AddWithValue("@REMARKS", remark);
                    cmd.Parameters.AddWithValue("@CLOSING_DATE", CLOSING_DATE);
                    cmd.Connection = con;
                    con.Open();
                    cmd.ExecuteNonQuery();
                    con.Close();

                    string PHONE_MOB = row.Cells[4].Text;
                    string SMSurl = "http://185.255.8.59/sms/1/text/query?username=NTpc&password=NTpc@321&from=MUNPLA&to= + PHONE_MOB + &text=Your OCMS Complaint No:" + COMP_ID + " has been resolved successfully - Meja Urja Nigam PVT. LTD. &indiaDltContentTemplateId=1207164466650628862&indiaDltPrincipalEntityId=1201159222154902387";
                    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(SMSurl);
                    HttpWebResponse response = (HttpWebResponse)request.GetResponse();
                    StreamReader sr = new StreamReader(response.GetResponseStream());
                    GridView1.EditIndex = -1;
                    row.Visible = false;
                }
            }
        }
    }
}