did you have a contract with them, if so go throught the smalls claims court on goods and service act it about 45 quid and you can do it on line at ur local county court, once you get the order, they got time to pay if they dont u can send bailiff, (loads of fun)
you need his full name, address, birth date contact no for a house, if you know where he lives, but not sure of the rest contact the land registery and they will sell you the details for about 2.50 or go council and look at vote registar this will give you details
whats the name of this company
i have used this route before when i was owned money from a previous business a lot of people dont like getting dragged to court, if he says that he doesnt live any where look at coucil tax records, driving licence or any bills that might be in his name, might mean a bit of work but in end is worth it, as far the courts are concerend if your on a council tax, you live there and bailiff can take what they need same goes for licence as they use the address on ur licence for law enforcement and can rule that, that is where they live (big brother state lol)