sql connection string error 'Unrecognized escape sequence'

private void btnsv_Click(object sender, EventArgs e)
{
    SqlConnection con = new SqlConnection("Provider=SQLOLEDB.1;Integrated Security=SSPI;Persist Security Info=False;Initial Catalog=tubd_data;Data Source=TIMY\SQLEXPRESS");
           
    try
    {
        con.Open();
        statusStrip1.Text="Connection Succesfull !!!";

        SqlCommand cmd = con.CreateCommand();

        cmd.CommandText="Insert into must_first [invoice_no], [date], [name], [total], [total_iv] values ('" + invo_no.Text + "','" + bill_datetxt.Text + "','" + txtname.Text + "','" + txttot.Text + "','" + txtvatinclu.Text + "')";
        con.Close();
        try
        {
            cmd.ExecuteNonQuery();
            statusStrip1.Text="Record Updated!!!";
        }
        catch(Exception)
        {
            statusStrip1.Text="Record Update Error!!!";
        }
    }
    catch(Exception)
    {
        statusStrip1.Text="Connection Fail !!!";
    }
}