As per case facts, the Petitioner imported Shrimp Larvae Feed, paying a lower customs duty. An investigation by DRI concluded that the goods were misdeclared, and a higher duty was ... applicable. The Petitioner, advised by DRI, deposited the differential duty and interest and requested the closure of the investigation, which was granted. Subsequently, the Petitioner sought a refund, asserting that later legal clarifications meant the lower duty was correct, and their payment during investigation was under protest. The High Court, after a previous remand, was tasked with deciding on the refund. The question arose whether the differential duty was paid under protest or voluntarily, if the subsequent clarification had retrospective effect, and if a refund was permissible without proving no unjust enrichment given the voluntary closure of investigation. Finally, the High Court held that the payment was voluntary, the subsequent legal change was prospective, not retrospective, and the Petitioner failed to prove no unjust enrichment. Thus, the refund request was dismissed.