Do you still live in the UK?
Well, that is a problem I'm afraid.
I suppose you dont have an address in the UK at all now?
No, that isn't the issue.
You do have a claim clearly. You can always sue at the small claims court.
To do so though you will have to have an address in the UK at which you can receive and have vision of any post. Otherwise the small claims court isn't available to you.
it doesn't have to be the address at which you live as long as you make that clear on the forms but it must be an address where you will see the post.
I don't know whether anybody at that address is able to check your post?
No court can enforce powers by itself. if they don't pay you have to get the subsequent orders like bailiffs or garnishing orders.
Getting the money is generally harder than getting judgment though if a debtor just refuses to pay.
All the best.