I would suggest heading for the airport at Benbecula first thing in the morning. The staff may be able to speak to Loganair directly rather than their or BA’s reservations.

Looking at the flight status section of the Loganair website for tomorrow, it seems that there is a LM471 departing for Glasgow at 10:40 and originating in Stornoway. Loganair announced last week that the Benbecula and Stornoway flights were being combined. It might be this has not been captured for the code share bookings.