I would take the matter to court as soon as possible.
I empathise! Be careful, though. If you do that, and your Polish isn't totally fluent, you'll have to legally hire a court interpreter. Guess how much that'll cost? I suggest you do something in their stupid office that, on the one hand, isn't serious enough to sue you, but annoying enough for them to send you a solicitor's letter. You can then reply to their solicitor in English, claiming your Polish isn't good enough (which is probably true), and that you demand a reply in fluent English for it to be legal. Write to their solicitors IN REPLY as many letters as possible by registered post, really dragging out each point in each letter and making it as long-winded as possible. Interpreters charge per word. It doesn't matter if the solicitor is an Oxford graduate; for his letters to be legally valid, they MUST bear the stamp of an official interpreter. That way those b*s*rds will have to pay through the nose. Oh and include some really long texts from "your Sri Lankan advisor", a long, long text in some obscure alphabet such as Sinhala. Additional, higher interpreter costs! Don't hire your own dollar-eyed solicitor, as you can't afford it. You haven't been paid. Good luck with those Catholics.