Booked an award trip on American AAdvantage. Paid a small amount for seat assignments on a short 2 hour leg on BA.

Later, I discovered that American was offering a Web Only Special that would save me 10,000 miles on the same flights. Rebooked it for the lower cost (haven't cancelled the first booking yet). However BA refuses to move our seat assignment to the new booking.

Their perspective is, "Tough luck! Doesn't matter if you're still on the same flight, but it's a different booking number".

My perspective is, "I paid for seats on a specific BA flight, I'll be on that flight, and I expect them to give me what I paid for".

So far, having zero luck with BA. It's not much money, but it's the principle of the issue. Anyone see a way around this?