Jquery Ajax call is not getting parameters values from textbox control

Below jquery ajax call is not working properly. IF I am directly passing values for city/area/vendortype then its working correctly. However below ajax call is not taking values from respective control.

public void GetVendors(int pageNumber, int pageSize, string city, string area, string vendortype)
    {
        List<VendorData> listVendors = new List<VendorData>();

        string cs = ConfigurationManager.ConnectionStrings["Connectionstr"].ConnectionString;
        using (SqlConnection con = new SqlConnection(cs))
        {
            SqlCommand cmd = new SqlCommand("spGetVendorbyFilter", con);
            cmd.CommandType = System.Data.CommandType.StoredProcedure;
            cmd.Parameters.AddWithValue("@PageNumber", pageNumber);
            cmd.Parameters.AddWithValue("@PageSize", pageSize);
            cmd.Parameters.AddWithValue("@city", city);
            cmd.Parameters.AddWithValue("@area", area);
            cmd.Parameters.AddWithValue("@vendortype", vendortype);


            con.Open();
            SqlDataReader rdr = cmd.ExecuteReader();
            while (rdr.Read())
            {
                VendorData vendor = new VendorData();
                vendor.pID = Convert.ToInt32(rdr["VendorID"]);
                vendor.pvendorname = Convert.ToString(rdr["VendorName"]);
                vendor.pcoverimage = Convert.ToString(rdr["CoverImage"]);
                vendor.pcategory = Convert.ToString(rdr["Category"]);
                listVendors.Add(vendor);

            }
        }

        JavaScriptSerializer js = new JavaScriptSerializer();
        Context.Response.Write(js.Serialize(listVendors));
    }

}


<script type="text/javascript">
        $(document).ready(function () {
            var currentPageNumber = 1;
            loadData(currentPageNumber);

            $(window).scroll(function () {
                if ($(window).scrollTop() == $(document).height() - $(window).height()) {

                    currentPageNumber += 1;
                    loadData(currentPageNumber);
                }

            });

            function loadData(currentPage)
            {
                var parCity = $("#lblCityParameter").val();
                var parArea = $("#lblAreaParameter").val();
                var parCategory = $("#lblVendortype").val();
                $.ajax({
                    type: 'POST',
                    url: 'WebService/VendorService.asmx/GetVendors',
                    **data: { pageNumber: currentPage, pageSize: 6, city: parCity, area: parArea, vendortype: parCategory }**,
                    dataType: 'json',
                   contentType: "application/json; charset=utf-8",
                    success: function (data)
                    {
                        var vendorRepeater = $('#repdata');
                        $(data).each(function (index,ven)
                       {
                            vendorRepeater.append('<div class="col-md-4 wow fadeInLeft animated" data-wow-delay="0.4s" style="text-align:center"><div id="Div1" class="living_boxauto" runat="server"><a href="VendorDetails.aspx?VendorId='+ven.pID+'"><div class="media"><img runat="server" class="img-responsive" src="images/'
                                + ven.pcoverimage +
                                '" style="width:300px;height:200px;" /><div class="media__body"><h2>Image Title</h2><p>Description</p></div></div></a><div id="Div2" class="living_desc" runat="server"><h3><a href="VendorDetails.aspx?VendorId='
                                +ven.pID+
                                '"><asp:Label ID="lblVendorName" runat="server" Text="'
                                + ven.pvendorname +
                                '" CssClass="lblVendorName"></asp:Label></a></h3><p></p></div></div></div>');
                        });
                    }
                });

            }

        });

    </script>