This depends on whether the mediation was set up through the Courthouse or with a private mediator. If it was through the Courthouse, you should be able to call the mediation department to obtain a new date. If it was a private mediation, you can file a Motion to Compel Mediation if you feel that is proper. Set it for hearing and have the judge order a date certain for the mediation.
One or two additional thoughts to add to what was said in the previous answer: Although mediation may have been court-ordered, ultimately it is a consensual process, in which the parties must agree on terms in order for there to be an enforceable agreement. Otherwise, the court will proceed to hear and determine the case. So, if mediation is likely to be helpful, it's worth pursuing. If, under the circumstances, it's merely a stage that has to be gone through in order to get to the next step in the procedure, then perhaps a properly-worded explanation to the judge might be helpful in moving things along. Also, you don't say whether you have an attorney representing you. If you do, your attorney should be able to do this for you.
Please note that I am not licensed to practice law in your state, and I practice only in NY. This response is provided for general educational purposes only, and no attorney-client relationship has been formed. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change. The response given is not intended to create, nor does it create an ongoing duty to respond to questions. As they say, "Your Mileage May Vary." Best of luck.