Hi Robert, to my knowledge, there is no zero-usage report like you can find in AT&T or other cellular vendors reporting.
I've gone through a lot of effort to try to aggregate all available data to really understand zero usage and because it's quite a challenge with high call volumes over time, I've fallen back to using the billing data to determine zero usage instead.
For our "My8x8" Billing Portal, I can download the "Download Service Summary (CSV)" from the "8x8 Monthly Statement" page.
In the 8x8_CustomerConsolidatedServiceSummary*.csv file - the headers "InPlan_Minutes, Intl_Minutes, Innetwork_Minutes" are the data points to look out for.