Hmmm, I was under the impression that email was collected to a schedule.AFter a quick check that would appear to be the case.

I'll see if it's supposed to be run on a schedule.
Your description isn't a catchall account. A catchall account is used to receive mail for an address that doesn't have a mailbox on your server. So if you had an email addressed to
123@yourdomain.com and that didn't exist it would get sent to the catchall account.
What you're describing for getting mail from your ISP account isn't easy (
AFAIK) using fetchmail or getmail. They're both meant to get mail from one or multiple external accounts and deliver them to a single mailbox. The mailbox you describe at your ISP is called a multidrop mailbox and are usually not a good idea as fetchmail etc tend to get confused by the headers on those emails.
Having said that you could always set-up the account on your server that mail is delivered to with a filter that forwards a copy to the correct recipient - assuming that there aren't too many.