Thanks a lot for the advice!
I’m not sure whether I should wait for an answer from AF to see if they would re-examine my case or proceed with the small claims court. When I bought the ticket they were selling premium economy for less than economy and if they were to calculate the 75% on the fare difference it would make things even more complicated.
My concern is that they are taking weeks to reply while at the beginning they were replying within hours/day, so I suspect they are just ignoring my emails.
I understand I could follow the small claims route even if I waited some more months? And from what I’ve read I can use the England and Wales court even if I live in Scotland?