Company A signed a contract with Company B on 1 January 2021. It was stated in the contract that the United Nations Convention on Contracts for the International Sale of Goods (CISG) is the governing law of the contract. Under the contract, Company A, as the seller, would deliver 10,000 tons of coal to Company B at the amount of USD100 per ton. The delivery date, as stipulated in the contract, was on or before 31 December 2021. On 1 June 2021, there was a sudden increase in demand of coal, and thus, the price of coal increased to USD200 per ton. Company A sought to renegotiate the price with Company B but Company B rejected the request. On 31 December 2021, Company A only delivered 5,000 tons of coal to Company B. Company B sued against Company A for damages. Advise whether Company A was liable for damages and whether Company A could rely on any defense under the CISG. Using the relevant CISG provisions and case laws (from any jurisdiction) to support your answer.