Notifications for payments of invoices that are Overdue by a certain amount of days

Notifications for payments of invoices that are Overdue by a certain amount of days

Basically, we're trying to come up with a way to automatically receive customized email notifications if a customer pays for an invoice that is at least 20 days Overdue. These emails would be different than the normal payment confirmation emails. We've not been able to find any straightforward way to do this in Books or Subscriptions. 

Any ideas would be greatly appreciate.

Thanks!