score:11
Flight schedules get changed all the time, some flights get cancelled, others get added. There is no law against it and no compensation available simply because they cancelled a flight.
As your flight is in the future, they have to give you a couple of choices: One you can cancel your booking and get your payment refunded; Two you can choose an alternate flight schedule between the two cities on the same airline.
If alternate times exist on the same day, the airline will usually automatically rebook you on another flight that day. If the flights goes only once a day or if they are dropping that city pair, then you will have to contact them in regard to how you wish to proceed.
As of this point, based on your posted details, the airline has done nothing wrong so there are no grounds that DOT can act upon. And rather than complaining to DOT you are better off getting in touch with the airline right away to see if an alternate time works for your vacation plans or cancelling completely and getting your money back. Sooner is better than later, because everyone else on the cancelled flight will be trying to grab alternate flights. And your window of opportunity for getting a refund is not open ended.