@pluralistic canonical help https://europa.eu/youreurope/citizens/travel/passenger-rights/air/index_en.htm
There are lots of ambulance-chasing keyword-squatting services which take a large commission but make it easy.

@celeduc So that is how to complain to the airline, but in this case, the airline's own complaint system has been replaced by a chatbot that doesn't work. I need to know how to complain ABOUT the airline, to the EC.

@pluralistic iirc you have to bring it to the "competent" national authority https://www.seguridadaerea.gob.es/en/consultas however... any claim has to be presented to the airline first. Although their website is *deliberately* borked to deter claims, the best way is to send overnight mail via Correos "burofax" to Vueling's address (Viladecans Business Park, Edif. Brasil, Carrer de Catalunya, 83, 08840, Viladecans, Barcelona) That's the first thing an ambulance chaser would do for you.