Cannot call button click event for a dynamic button

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C#

ASP.NET

I am using a dynamic buttons which are genertated on the click of a asp calender date and i want to write code on the click event of the dynamcic controle But now when i click on the button the button disapeares.

I also called this event on the page load

What I have tried:

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        Doctor();
        Department();
        Bind();
        FillAppointmnetGrid();
        month.Visible = false;
        DateTime sDate = Calendar1.SelectedDate;
        string doc = ddlDoctor.SelectedValue.ToString();
        GenerateDocSlotLabels(doc, sDate);
    }
    //this.BindGrid();
}

protected void Calendar1_SelectionChanged1(object sender, EventArgs e)
{
    try
    {
        DateTime sDate = Calendar1.SelectedDate;
        string doc = ddlDoctor.SelectedValue.ToString();
        GenerateDocSlotLabels(doc, sDate);
    }
    catch (Exception ex) { throw new Exception(ex.ToString()); }
}

protected void GenerateDocSlotLabels(string doc, DateTime sDate)
{
    doc = ddlDoctor.SelectedValue.ToString();
    sDate = Calendar1.SelectedDate;
    string sDay = sDate.ToString("MM/dd/yyyy");
    DataTable dt = tsbll.GetAvailableSlotsbyDocAndDate(doc, sDay);

    foreach (DataRow dr in dt.Rows)
    {
        Button label = new Button();
        label.Text = dr["SlotTime"].ToString();
        //label.Style["Left"] = "20px";
        label.CssClass = "btn btn-primary";
        //label.CssClass = "background - color: #19bc49;";
        label.Click += new EventHandler(labelClick);
        pnlLabel.Controls.Add(label);
    }
}