Purchased Seats Given Away

I purchased upfront seats on a flight from Singapore to Shantou. My seats were given away by Jetstar on both the outward leg and the return journey. It seems to me that since these seats have to be paid for, Jetstar could have collected the upfront fees twice. Has anyone else had this experience? It was bad experience, as the seats were for my elder parents and caregiver. The seats I purchased were together and aisle seats. The ones they allocated were separated from each other, further back, and non-aisle. Buyer beware.