The ledger
Every movement, with the reason. Purchases, deductions, refunds — each carrying the feature that caused it and what it belonged to.
Attribution
Deductions are attributed to the position and the candidate they were spent on, so "what did filling this role cost" is a question with an answer rather than an estimate.
Monthly statements
A statement per month: what was spent, on what, and how it compares with the month before. Demo runs and candidate practice appear nowhere on it, because neither is billed.
When a number looks wrong
Two things to check before concluding it is a bug.
The window. A figure covering a longer period than you assumed is the commonest cause of surprise, and the date range is on the page.
Multi-stage flows. Credits are charged as candidates advance, so a month's spend on a flow reflects who progressed that month rather than who was scheduled.
If it still looks wrong, the ledger is itemised: find the deduction that does not belong and open a ticket quoting it. A specific line is answerable; a total is not.