Don't be so hard on yourself, OP
I know these things can be annoying...and suppose they can work themselves out in a number of ways. My understanding is that BA now send an email about seat changes...
In the days before I was introduced to FlyerTalk, I had been bumped from 62A to a middle lower deck seat without knowing, and only realised on check in. It was annoying, and nothing could be done to get me a seat on the upper deck. The story ended up with my new seat table being at such an angle there was no way of getting any work done or eating. After a nice conversation with the CSD during boarding they gave me the choice of 1A and K - cue, my first thread on FT
Back on topic, it does seem the Gatwick fleet is more prone to these changes, than elsewhere.