Overdue invoicing mail, bill and invoice


I have some questions.

  1. Why overdue invoices are not sent by email? I have verified the sourcecode of cron.php and iit only uses recuring date, not the overdue periods of invoices. I hhave set all email templates but also nothing.

  2. I make an invoice and give it a number. It is possible that on payment to change it and transform the invoie into bill or billed with another number and series?