In cases of flight delay, cancellation, or denied boarding (being refused on a flight), the airline must provide free necessary material assistance to passengers according to the waiting time at the airport, starting from the moment the delay, cancellation, or interruption of the flight occurred.

From one hour: Assistance for communication (internet access, phone calls, etc.).

From two hours: Assistance for food (vouchers, snacks, drinks, etc.).

From four hours: Assistance for accommodation or lodging if the passenger does not reside in the local area, and transportation from the airport to the accommodation. If the passenger resides locally, the airline may only offer transportation between their residence and the airport.

Exceeding four hours: Offer rebooking options or a refund.

Throughout this process, the airlines must keep passengers informed of the estimated departure time for delayed flights every 30 minutes.

Passengers with Special Needs (PNAE) and their companions are always entitled to accommodation, regardless of the requirement to stay overnight at the airport.

The airline may suspend the material assistance in order to proceed with immediate boarding.

It occurs when a passenger is denied boarding by the airline, even after they have fulfilled all the necessary requirements to board the aircraft. This usually happens due to the substitution of the scheduled aircraft with a smaller one, or when the aircraft needs to fly lighter due to operational safety reasons, or when ticket sales exceed the aircraft's capacity, known as overbooking.

In all cases, once the airline realizes the possibility of denied boarding, they should seek volunteers who are willing to be rebooked on another flight, offering compensations such as cash, extra tickets, miles, hotel accommodations, etc. 
The airline may ask the passenger to sign a receipt as proof of accepting the offer. If the proposal is refused, the airline is responsible for supplying alternative rebooking options, refunds, and necessary assistance.

First, you should contact the airline's customer service channels. If the problem persists and you believe your rights have been violated, you can contact the appropriate channel at the National Civil Aviation Agency (ANAC) to file a complaint. All airlines operating in Brazil are registered on this platform and must respond to complaints. ANAC monitors the registry and the service provided by the airlines on a collective basis. It is important to keep documents such as boarding passes and receipts for expenses regarding food, transportation, accommodation, communication, and other aspects related to the contract signed with the airline. 

To claim compensation for moral and/or material damages, you should consult Consumer Protection organizations or approach the Judiciary. It is important to keep documents such as boarding passes and receipts for expenses regarding food, transportation, accommodation, communication, and other aspects related to the contract signed with the airline.