If you believe you are legally entitled to money (you agreed upon a payment) or didn't assign copyright, you can sue them. I don't know where you are, but in th

If you believe you are legally entitled to money (you agreed upon a payment) or didn't assign copyright, you can sue them. I don't know where you are, but in the UK for example, the small claims court handles cases like this (up to £10,000 of damages), and it's a case of filling out a form and sending it off, you don't need to have a lawyer but it's sometimes advisable. From the Intellectual Property Enterprise Court guide: "The IPEC small claims track is designed to be used by parties who do not have a legal representative acting for them. Accordingly it has more simplified procedures than a standard civil claim...". I would advise looking at what small claims options your jurisdiction provides.