A misunderstanding and not comprehensive at all

Due to sandstorm in November 2018, more than 40 flights have been cancelled. My boyfriend had to go with an another airline company in GC for a big Pacific tournament. Unfortunately, they delayed our friday night flight to a Sunday 10am flight. It was too late for the tournament. So we went to Jetstar counter and asking if they had a flight before sunday morning. The man said 'we have a flight at 6'. We buy it directly in cash $821 for a one way only. Prices were very expensive regarding all flight delays but we had no choice, my boyfriend trained for 1 year and did many diet for this tournament He printed the boarding pass and on the path, we saw boarding time was at sunday 6pm not 6am. My boyfriend has directly saw the man, who said 'I told you it was 6pm not am'. As they were a huge queue, we decided to line up and wait for our turn. After 20 minutes of waiting, it was almost our turn, the man left its office and a women replaces him. We explained her our story and asked for a sooner flight. She said that this is impossible, all flights are booked. So we asked for a refund. She said that they don't make refunds, only credit voucher. As we are french, I explained that there were a misunderstanding, that we bought flights less than an hour, the money is still in the cash register, the cash is our holidays budget. So she went to see the man and her manager. After few minutes, she came back and confirm us that we can't be refund and there is no credit voucher either because the tickets are not refundable.
So we lost $821, we didn't take the plane. They could take advantage of this situation and could propose these tickets for other people. Since the airport was full of people which their flights have been cancelled too. The salesman were not helfull at all, not comprehensive, mostly that we are french and it was a communication mistake. We will never fly with them. NEVER !

Australia-Gold Coast