Paramount, it’s SOP that a new company would take over the old company’s clients. You should visit them in person and tell them that you wish them well but that you’ve decided to self-manage for time being. If they owe you money, try to get it back. Maybe you can work out a deal with the new management? Who knows, after meeting the new people in person you may decide to give them a chance to earn your business.

If you don’t want to work with them, and they don’t want to refund your money, you could still go to small claims court.