Approach some solicitor's for a quick chat, for some free advise and see if they can offer you any guidance as to your chances of retrieving your money. They should hopefully give you 5 minutes of their time. You could also try the citizens advise bureau but this would probably be out of their depth
Do not antagonise FTE just yet. Perhaps, if you can not recover your deposit, the money could go towards the cost of say an IR with them if you were to go down the modular route.
Good luck, I hope this does not prove to be an expensive life lesson.