AutoComplete showing wrong names when alphabets is typed

 my AutoComplete is not showing the right names when i type alphabetes.

For example, if i type M it will show autocomplete of names with M, if i add c to M it will show names with MC. but my autocomplete is not that way, if i type M sometimes it doesnt show the names with it

 <script type="text/javascript">
     $(function () {
         $("[id$=SearchText]").autocomplete({
             source: function (request, response) {
                 $.ajax({
                     url: '<%=ResolveUrl("~/Default2.aspx/GetNames") %>',
                     data: "{ 'prefix': '" + request.term + "'}",
                     dataType: "json",
                     type: "POST",
                     contentType: "application/json; charset=utf-8",
                     success: function (data) {
                         response($.map(data.d, function (item) {
                             return {
                                 label: item.split('-')[0],
                                 val: item.split('-')[1]
                             }
                         }))
                     },
                     error: function (response) {
                         alert(response.responseText);
                     },
                     failure: function (response) {
                         alert(response.responseText);
                     }
                 });
             },
             select: function (e, i) {
                 $("[id$=hfUserName]").val(i.item.val);
             },
             minLength: 1
         });
     });
</script>

code

public partial class Home : System.Web.UI.Page
{
    [WebMethod]
    public static string[] GetNames(string prefix)
    {
        List<string> users = new List<string>();
        using (SqlConnection conn = new SqlConnection())
        {
            conn.ConnectionString = ConfigurationManager.ConnectionStrings[""].ConnectionString;
            using (SqlCommand cmd = new SqlCommand())
            {
                cmd.CommandText = "select Name, UserName from User3 where " + "UserName like @SearchText + '%'";
                cmd.Parameters.AddWithValue("@SearchText", prefix);
                cmd.Connection = conn;
                conn.Open();
                using (SqlDataReader sdr = cmd.ExecuteReader())
                {
                    while (sdr.Read())
                    {
                        users.Add(string.Format("{0}-{1}", sdr["Name"], sdr["UserName"]));
                    }
                }
                conn.Close();
            }
        }
        return users.ToArray();
    }