Diagnosing a Settings Page Nobody Can Navigate

Support tickets consistently say some version of "I can't find how to turn off notifications" for a product whose settings are actually organized as: "Account" (login, password, linked devices), "Billing" (plan, payment method, invoices), and "System" (notification frequency, data sync, storage limits, API access) — a structure that mirrors the three engineering teams that own those areas internally.

1. Using Indi Young's mental-model/system-model framing, diagnose exactly what's wrong here.
2. What research would you run to find the user's actual mental model for these settings, and what would you expect it to reveal?
3. Propose a revised structure, and explain what principle drove the regrouping (not just the new labels).
4. Why would simply renicknaming "System" to something friendlier, without regrouping the items inside it, likely fail to fix the complaints?