If Frontier cancels a flight or makes a major schedule change call at passengers are entitled to a full refund. However, if a passenger decides to cancel their flight, the cancellation will generally only apply if the flight is canceled after 24 hours and at least seven days before departure.
Source: https://www.devex.com/people/como-hablo-con-una-persona-real-en-expedia-expedia-army-2075484
