I cancelled a one way SYD-MEL-LHR itinerary (QF metal, obv.) online, 4 days ago. Had to fill out the long form rather than the normal form which tells you how much you'll get back etc. The booking disappeared from my BAEC "my bookings" list but is still visible as confirmed+ticketed on checkmytrip.com. Have had no Avios or cash back yet. Last time this happened, I called up after a week and the CS agent told me there was no record of me ever having even tried to cancel it and processed it immediately on the phone.