Infelizmente, a EasyJet não reembolsa permissões de bagagem não usadas e de acordo com os Termos e Condições (ênfase minha):
Add hold luggage, sports equipment or increase your weight allowance
You can add new hold luggage or sports equipment, or increase your weight allowance. Just log into Manage Bookings or our mobile App and select the 'Add hold luggage' option. You’ll need the email address and password used to make the original booking.
We’re unable to refund luggage allowance you’ve already bought.