Hi,
I am also using v7.1.3.1, and hae had the same issue.
I emailed tech support, and here is their reply - and it worked
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You will need to log into the Administrator options. Once logged into the administrator options on the very top select Automated Tasks. A smaller screen will open under the tasks on the left hand side select Unbilled Charges Report. Uncheck the task Enabled check box and select OK.
Once this is unchecked it will turn off the unbilled charge report from appearing in your messages daily. You can still access this report if needed under Billing on the front screen reports.
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