In order to view Net Billings by Plan, your best bet is to download the Adjustments export from Analytics --> Exports in your Recurly UI.
1) Filter the adjusment_type column to only show charges.
2) Filter the plan_code column to only show a specific plan so you can calculate the total for each one separately by using the adjustment_total column.
3) Once you have done that, go to the adjustment_refund column and filter to only show TRUE, so that you can only view refunds. Calculate the total of refunds via the adjustment_total column.
4) Subtract the refund total from the charge total to get your net billings for that specific plan. You will need to repeat this step for each plan_code.