Are you registered with the PRTB? If so, might be worth chasing through this way, but from everything posted before, this will take time. But I don't think it will cost you any cash (only stress!!).
Other than that, you could go after them yourself, but that will involve solicitors & may be good money after bad. How likely are you to get the money even if you get a judgement in your favour?
I would reckon it is only the guy you could go after as he is the only one who signed the contract, but a legal person may be able to advise on this point.