Collecting on bad debt is difficult and time consuming. For the amounts you've mentioned, you can move on and make it up quickly enough as gp stated. If they don't want the work you've done, offer them a 30 day transition period so you both can move on. I would suggest you attach some form of payment to that, but it might just be better to give them control of their domains w/o your work product and call it a day. Next time, get proper contracts in place. Recognize that even with a proper contract, it would still be difficult to collect. Time & Effort vs. Reward.