Dot Matrix Printer Does Not Resize Paper Size

I am using a dot matrix printer for receipt printing. I installed the same as Generic only text. But I send the print, it recognizes the height as A4 paper. How do I get the printer to cut paper when there are no characters.

Here is the code used:

 public class CPrint
    {
        protected StringReader stringToPrint;
        protected Font printFont;

        public int altura { get; set; }

        public int tam { get; set; }


        public CPrint()
        {
        }


        public void PageCreate(string printerName, string file)
        {
            CFormatacao formatar = new CFormatacao();
            StringBuilder sb = new StringBuilder();
            string qs = "";
            //try
            //{
                string texto = "";
                int qtdLinha = 0;
                StreamReader arq = new StreamReader(file, System.Text.Encoding.Default, false, 512);

                while (!arq.EndOfStream)
                {
                    texto += arq.ReadLine() + System.Environment.NewLine;
                    qtdLinha++;
                }

                //for (int i = 0; i < 10; i++)
                //{
                //    texto += System.Environment.NewLine;
                //}

                texto = formatar.RemoveAcentos(texto);
                altura = qtdLinha +10;
                arq.Close();


                stringToPrint = new StringReader(texto);
                printFont = new Font("Arial", 12);

                PrintDocument doc = new PrintDocument();

                doc.PrinterSettings.PrinterName = printerName;

                tam = 827 * altura;
                tam = formatar.ConverteEmInteiro(Math.Round(tam/75M).ToString());
                //Configura um novo papel
                PaperSize ps = new PaperSize("MT", 827, tam);
                doc.DefaultPageSettings.PaperSize = ps;

                doc.PrintPage += new PrintPageEventHandler(this.PagePrint);
                // print the page
                doc.Print();
                stringToPrint.Close();

                qs = "~/frmMensagem.aspx?msg=Recibo Impresso!";



            HttpContext.Current.Response.Redirect(qs);
        }



        private void PagePrint(object sender, PrintPageEventArgs e)
        {
            float linesPerPage = 0;
            float linePosition = 0;
            int lineCount = 0;

            float leftMargin = 5;
            float topMargin = 5;
            String line = null;

            linesPerPage = altura;//e.MarginBounds.Height / printFont.GetHeight(e.Graphics);
            //linesPerPage = e.MarginBounds.Height / printFont.GetHeight(e.Graphics);

            while (lineCount < linesPerPage && ((line = stringToPrint.ReadLine()) != null))
            {
                linePosition = topMargin + (lineCount * printFont.GetHeight(e.Graphics));
                e.Graphics.DrawString(line, printFont, Brushes.Black, leftMargin, linePosition, new StringFormat());
                lineCount++;

                if (true)
                {

                }

            }
            line = null;

            if (line != null )
                e.HasMorePages = true;
            else
                e.HasMorePages = false;

        }
    }