We obviously need a way to prohibit accounts from being closed when there is a pending dispute.
Although you can choose to keep the account open with a zero balance, Reg E prohibits you from stopping a customer from using or withdrawing provisional credit during your investigation.
In you case, depending on your bank's accounting practices, you can reopen the account to overdraw it when you debit the provisional credit and then charge the account off. Since your customer owes you the money, you can report them to a credit reporting agency/chexsystems as your procedures dictate.
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