Han Yu has a strawberry farm on the outskirts of Melbourne. He contracted to sell 200kgs of strawberries to Julie who has a jam factory in Richmond, Melbourne. The strawberries are to be delivered on 1 August 2020. The contract price was $2000 of which $500 was paid in advance by Julie. Just before sunset on 31 July, Han Yu picks the strawberries and loads them in his truck to deliver to Julie's jam factory the next day morning. Unfortunately, that night there is a fire in overhead power lines near Han Yu's house and the power lines fall on the main road that connects Han Yu's house to Richmond, Melbourne. The emergency services say that it will be a week before the fallen power lines will be removed and the roads reopened. Han Yu cannot drive to deliver strawberries as promised and informs Julie about it. Julie is upset and asks Han Yu to return the $500 that she had paid to him.Han Yu refuses to return the money.

Please advise what remedies are available to the parties under the contract law. Cite relevant cases.