The money is gone, and actually, for them, it isn't even about the money - it's about the drama and the money is what they are currently using to keep you hooked into them. And thus available for drama.
So my advice would be to consider how much drama you enjoy.
If you are a mega drama-llama, then yay! Take them to court, report to HMRC, stay hooked in to the drama and the shenanigans. It will last for years, and may never end.
Or if you hate drama, consider the money as the price of several life lessons learned. Go No Contact with them and end the drama. I promise, this will be more of a punishment to them than any other action you can take. It will also be the very best way for you to have the peace to hel from your childhood trauma.
All forms of abusive relationships are addictive, and you may find you are more addicted to the drama cycle than you think, so be really honest with yourself. But you will not get back that money, whatever you choose to do.