Booking.com Refused to Refund My Cancelled Qantas Flight

I am writing regarding a serious problem with a flight booking I made through Booking.com. I had booked a Qantas return flight from Brisbane to Singapore and then on to Heathrow, scheduled for 30.03.26, using Booking.com. On the day of travel, the Qantas flight from Brisbane was cancelled, and Qantas changed me to an Emirates flight instead. Despite this change, I was still left to sort everything out myself. Because my original Qantas flight booked via Booking.com was cancelled and I was moved to Emirates, I had to buy a new ticket directly at the Qantas desk that same evening in order to complete my journey. This meant I paid once for the original ticket through Booking.com and then again for a new ticket at the airport. I have tried multiple times to contact Booking.com and Booking.com/help about this, but I have not received any useful support or resolution. I was given a new code today, but despite this, I still do not have my refund or any clear response. I am requesting a full refund of the original Qantas ticket that I purchased through Booking.com, and I also want Booking.com to cover the extra cost of the new ticket that I was forced to buy at the Qantas desk that evening due to the cancellation and change to Emirates. I expect Booking.com to review my case, contact the airline if necessary, and reimburse the amounts I paid so that I am not left out of pocket for a situation that was completely outside my control.