Priceline / Hertz review: Car rental

We had a trip booked flights and car rental but had to change the dates. we Had to cancel our flights and rebook have not seen a refund for flights But Priceline would not refund the car rental $550.00 Herts said it was ok with them But Priceline refused to cancel the reservation insuring that they could charge us for the rental. this is theft. Herts says they have a contract with Priceline and can't cancel the rental. To me that make Hertz complicit in this.