This article explains how to post an Office Cancel Bill in Insight™ Legal.

If a Bill has been posted to the ledger, it can be cancelled as long as it has not been partially paid or paid in full.

To cancel an unpaid bill, follow the steps below:

Go to Accounts, then select Clients.
Search for the Matter Ledger on Matter Lookup.
On the posting tab select O8 Cancel Bill from the drop down list of posting types.
Ensure that the date you wish to cancel the bill is entered correctly and then select the Bill you wish to cancel.

If the bill does not appear on this screen this means that it has been paid and is not available to cancel.
Once the bill has been selected then click on Post. This will then show the bill as cancelled on the ledger and in the Bills tab. The ledger will then show the amount of the Bill being credited to the ledger and a credit note will appear in the Bills tab.
Once the Bill has been cancelled it will then be removed from your Outstanding Bills and Aged Debtors reports