CANCELLATIONS
All customers whose flight is cancelled by JetBlue will, at the customer’s option, receive a full refund or reaccommodation on the next available JetBlue flight at no additional charge or fare. If JetBlue cancels a flight within 4 hours of scheduled departure and the cancellation is due to a Controllable Irregularity, JetBlue will also provide the customer with a $50 Credit good for future travel on JetBlue.

It looks like JetBlue did exactly what they show in the Bill of Rights. They reaccomodated you and also gave you $50 credit just as you said. It seems you interpreted this incorrectly.