In the not so distant past I'd booked a late notice day trip on the app, which unfortunately managed to go through twice (double tapped on the app no doubt)... and ticketed both (took the money twice on my card) - both in my name too but under separate PNR's.
Luckily a quick call to BA managed to cancel one off, but it did make OLCI very difficult for a while - after calling them, the one 'good' booking refused to OLCI on MMB until I'd almost got to the airport, but luckily I had managed to get seats.