Write to [email protected] — a real person reads it, usually answering within two business days.
The app version (Settings → the version line at the bottom), your phone model, and what you expected to happen. In Settings there is Send feedback, which attaches the app version, the platform and the in-app log to the message — it tells you exactly what is being sent before it goes.
By design. Sound through walls tells you where it is loudest, not where the pipe is broken. Claiming otherwise would cost you a wall.
No. A cheap piezo disc improves the signal and the app explains how to use one, but it is optional.
Purchases are handled by the store, so refunds are requested there: on Android through Google Play (Order history → Report a problem), on iOS through Apple (reportaproblem.apple.com). If a refund is refused and you believe the app is at fault, write to us anyway — we would rather refund you than argue.
What the app does with data is written out in full on the privacy page.