Wa Alaikum Assalam, Achraf.
I understand you are going through a difficult situation. Regarding the refund, it largely depends on the terms and conditions of the Hajj contract you had with Nusuk. In addition, the banking laws and consumer rights laws in Saudi Arabia also come into play.
According to Article 42 of the Saudi Arabian Monetary Authority (SAMA) law, customer complaints regarding banks should be resolved promptly and banks "shall have in place effective and sound complaint management processes relating to its services, operations, and its banking professional conduct".
Also, under Saudi Arabian law for consumer protection, Article 16 mentions that "If it is proven to the Committee that there is a defect in the commodity or the service, the Committee shall oblige the supplier to refund the price to the consumer against returning the commodity to him otherwise to compensate him for the deficiency of the commodity unless the supplier can remove the defect and the consumer agrees to that."
However, in this case, your parents did not receive the service due to a timing issue rather than a defect on part of the service provider. The refund policy would be largely dictated by the terms and agreement made with Nusuk initially.
For immediate assistance, I advise that you reach out to SAMA (Saudi Arabian Monetary Authority) to file a formal complaint regarding the delay in the refund, making sure you explain the situation in detail and the urgency of the case.
Please remember that my advice is only based on your description and the law. It is always advisable to consult with a legal professional for personalized advice.
May Allah ease your difficulties, and I pray that your concerns get resolved soon. Ameen.