It's hard to answer this question completely without the specific details, but I will do my best.
First, you probably do not have a warrant out for your arrest. Even if you were required to do certain things on unsupervised probation, many times it falls through the cracks and nobody notices. If you are on supervised probation, your probation officer would probably warn you that you were risking being violated. I do not see you being forced to go to jail for not completing your alcohol classes.
Second, whether or not you can complete it or how you should complete it are most likely issues between you and whoever you paid to handle the class. There are many companies that do alcohol classes and honestly they do not care about you or your drinking, they just want your money. Even if this particular company will not return your phone calls, you can always get another assessment and start over with another company.
Third, I do believe you will have to show you have gotten an assessment and complied with its recommendations before DMV will give you your license back. As such, you may want to find a different company and start over with them. Get a fresh assessment and start the classes over again if you cannot get in touch with your original company. I know it would be frustrating to pay the money and do the classes over again, but it will not be worse than not being able to get your license back.
If you had an attorney for the first charge and plea, you need to contact them and see if they can help. If you are attempting to complete the requirements of your probation the court will likely extend your time, but you need to be prepared to show why you didn't complete it in the time granted. Time is of the essence, so if you can contact your original attorney today and start the process.
If you did not complete the treatment in a timely manner, then you will need to have a new assessment and start the treatment over. You will not be eligible for a license until you have completed everything and the 508 form is sent to DMV from the assessing agency. Any limited privilege you have had expires one year from the date of your conviction. It CANNOT be extended while you complete the classes, so you are not eligible to drive after it expires.
Mecklenburg County has a somewhat unique protocol re: non-compliance with a condition of the judgment. One key question is: How Much Time Has Expired?
Community Service and Alcohol Treatment issues are relatively common. Fines & Costs payment can also pose problems; but, often times those are addressed in the Fine Collection Payment Program. . .at least in Mecklenburg County.
Post Judgment Services, which is located on the 4th floor of the Criminal Courts Building, is charged with signing up people for Community Service, Fine Collection, Assessment / Treatment Compliance, etc. They also keep track of the progress of people Ordered into the respective programs.
Frankly, they're pretty aggressive in following up and in certain instances and will refer the matter back to Court for review. In fact, there are cases where non-compliance can actually result in an Order for Arrest (OFA) being issued by the Court. (For example, if the person fails to even show up to Post Judgment Center after the judgment, an OFA can issue.)
The alcohol class providers can be a problem. It depends on the company handling them. Timing is key and without more information, it is somewhat difficult to know where things are in the process. In the question posed, all but one class has been completed. That certainly doesn't hurt.
Having said that, if it seems to be developing into a problem, an Attorney can "add-on" the matter for a Compliance Hearing and request the Court to extend the time for completion of classes. Again, timing, or better said, the amount of time that has expired, is key.
At a hearing, Counsel would want to present evidence of the efforts to comply and suggest a realistic time-frame for completion. It may also serve as an indication of the Court of the proactive attempts to comply.
Given the complexity of such matters and assuming an attorney was involved, it makes sense to consult with the lawyer whom handled the case at trial / plea.
NOTE: Although a response is provided to the specific question, there may be other facts and law relevant to the issue. The questioner should not base any decision on the answer and is specifically advised no client-lawyer relationship has been established. Put simply, seek the advice of competent counsel without delay to discuss the particular aspects of the case, factual scenario and historical background.