EU directive 261 specifies under which circumstances compensation must be paid to passengers for cancelled and delayed flights. The amount is determined by the distance. It’s a straightforward process to make a claim and it shouldn’t be necessary to have any legal assistance. There are a multitude of companies online will do the work, for a fixed price, usually a percentage of any payment made by the airline.
I recently had a flight cancelled from Mexico to Europe and was rebooked on a flight 3 days later. EU261 means that the airline has 3 options, reschedule on another flight with any airline, rebook and pay for food and accommodation, refund. I flew on the same day as my cancelled flight after buying a ticket on another airline. I just received 600 Euros compensation plus 595 Euros for the cost of the ticket I bought. It was a very easy process and I had a response with 10 working days.
If I can help anyone please ask. I can provide some links to online resources that may help others.