Simply make a request for a refund because your flight. Wait 7 days and on the 8th day (unless you are advised that a refund has been processed), initiate a chargeback with your credit card issuer (bank).

Do everything in writing and keep copies or screen shots. If you submit a chargeback, have a copy of your e-ticket receipt, the cancellation/rescheduling notice, your request for a refund, and the refund denial or a note than there has been no response.

EC 261/2004 has not changed and even if the EU were to do so, to the extent that you and your bank are located in the UK and your ticket originates there, the Regulation has been enacted into UK law and thus stands unless Parliament, as opposed to the EC amends it.