Three suggestions:
1. Focus,
2. Focus, and
3. Focus.

You have wasted a year. As you have learned, the CAA has now told you what you think you knew a year ago and based on what you told the CAA. It also has the ontime flight data, so going back and telling the CAA what it already knows is a pointless waste of your time and frankly will simply fill a trash bin somewhere as it is irrelevant.

The sole question is whether EC 261/2004 applies to you in a specific situation and if not promptly paid whether you are able to obtain enforcement in a UK court. As you have not supplied any details ("liability to the delay" does not mean anything in the language of EC 261/2004) that is about it.

Presuming that you are a UK resident, go ahead and start the MCOL process. The forms are available online and the process is fairly simple so long as you follow it carefully. If you are entitled to your EUR 600, you will see it in due course. If you are not, you won't.

If you want better advice, then provide better detail. Air carrier and the exact specifics of the delay/cancellation and how it is that the carrier has admitted "liability to the delay" but won't pay.

If you think that anyone is fining anyone, forget it.