It sounds like your obligations are over but of course it depends on the specific facts. The credit card company obviously sided with you and refunded your money. The merchant may believe they are entitled to the money and so they can always sue you. Reading between the lines it appears that you hired a merchant to perform services for you and either they failed to perform or they performed them unsatisfactorily. There may be a dispute regarding whether one party lived up to their end of the deal, but this would likely have to be resolved in court.
This is not to be considered legal advice nor does an attorney-client relationship exist.