I do custom software development for a customer. That customer takes the software that I write for them, and resells it to their customers. My customer is unable to pay their latest invoices, however they still continue to resell what I have written for them (including portions they haven't paid for). What can I legally do to recoupe my investment? I assume I can sue them for the unpaid invoices, but am I also able to restrict them from reselling the software with the included portions wich are unpaid?