In Parallels H-Sphere terms a user runs into debt when their account negative balance exceeds credit limit.
When users run into debts, they are automatically blocked from buying more resources. Except for this, the functionality of the debtor's account isn't affected. If you find this insufficient, use billing balance report to track down debtors and warn them with mass mail of expected punitive measures if they fail to pay off the debt. When the period to pay off the debts expires, you can suspend their account. This will close access to their control panel and display a Suspended page to their site visitors. If the debt is paid by check, you credit the paid amount and resume the account. If the debt is paid by credit card, the account will be resumed automatically. If the debtor fails to pay the debt, you can delete their account along with user's home directory content.
You can configure Parallels H-Sphere to apply punitive measures to debtors automatically:
Notes: leave the days box empty, to apply enabled measure immediately without any prolongation periods.
If you want to change the date since when the system starts treating user as a debtor to apply punitive measures to: