Populate TextBox from database based on particular user in ASP.Net

How do I populate textbox from database based on parameter.

For example I don't want all the data in the database to populate. I just want particular data from a particular user, so I used parameterized query.

But it is not working, all the data in the datbase still populates. Please how can the query be well written?

I used a web method to populate values from database.

public static List<string> SearchCust(string prefixText, int count)
{
    using (SqlConnection con = new SqlConnection())
    {
        con.ConnectionString = ConfigurationManager.ConnectionStrings["ConString"].ConnectionString;
        using (SqlCommand cmd = new SqlCommand())
        {
            cmd.CommandText = "SELECT [Id], [Tname] FROM [InvoiceTable] where [Tname] LIKE @SearchText + '%' AND CreatedBy = @CreatedBy";
            cmd.Parameters.AddWithValue("@SearchText", prefixText);
            cmd.Parameters.AddWithValue("@CreatedBy", createby.Text);
            cmd.Connection = con;
            con.Open();
            List<string> BioCust = new List<string>();
            using (SqlDataReader sdr = cmd.ExecuteReader())
            {
                while (sdr.Read())
                {
                    BioCust.Add(AjaxControlToolkit.AutoCompleteExtender.CreateAutoCompleteItem(sdr["Tname"].ToString(),
                    sdr["Id"].ToString()));
                }
            }
            con.Close();
 
            return BioCust;
        }
    }
}