If you, like every other freelancer on the web it seems, have trouble getting them to pay you, do a claim on the small claims court - you have to prove that you have made efforts to get payed so make sure you ask them first, and then after they send you a few evasively nonsensical emails just fill out the form online and pay the charge (it depends how much they owe you how much you have to pay, it can be as low as 25 pounds). It worked for me straight away, it takes minutes to do, and they have to pay you back the charge too so its win all round!