I was delayed on an IBERIA flight from LHR-MAD for a mechanical which resulted in me missing my MAD-JFK flight. they refused to route me any other way and booked me for the next day. I filled out a compensation form at the airport, as well as online after my trip. They only ever received the online one. after some time I was denied the compensation because they claimed it was beyond their control. I wrote to the Spanish aesa. after 2 months they responded that because it occurred in the UK, I would have to reach out to the UK CAA. I then filed a complaint to the CAA. now its 2 and half months later and Iberia finally contacted me to say that they reviewed my case and they will pay it and asked for my bank details. I would tell anyone else, don't give up, eventually it will pay off.