I emailed a few people at the top of management after getting nowhere with the phone and chat support. I didn’t hear back, so I followed up with another email. Today, I finally received a response saying that someone from Customer Service will be in touch. Hopefully, I’ll get this resolved sometime this week.

I did inform FB that I no longer have the boarding passes, as I usually dispose of them about a week after returning from a trip.

One lesson I’ve learned from this is to always keep boarding passes and regularly check FF accounts. I hadn’t realised how many trips were missing from my FB account - some trips only had one leg credited, and in other cases, the entire trip was missing.