Unauthorised Ticket Refund

I booked a return flight with Booking.com in August 2024. Due to unfortunate circumstances, I had to change the flight booking, I called the airline and asked to put my ticket on hold and cancel that flight, which they did and which is normal procedure when wanting to change flights done through Booking.com, as stated by their policy. In June 2025, I tried to use the ticket and the airline informed me the third party (Booking.com) had requested (on 5 February 2025) and received (on 6 February 2025) a refund for that ticket, and therefore it was no longer valid. The airline also provided evidence of said process. I did not request a refund, neither was I aware that Booking.com did that, or get any of that money. I called customer service on 10 June 2025, to make an enquiry, they asked me to send evidence of the things I had to prove my case so it can be resolved, I did, I even sent a follow up email on 11 June 2025, with no response. On 2 August, I made another enquiry with customer service, they made me go through the exact same process, and I still comp****, still with no response. I also send a formal letter of demand to their support and customer service, with no response. I attempted to use the chat in the app, and I was assured my matter was being resolved, only to be given a link to “submit my grievance” but the link is meant for people who have listed property on the app, and not consumers. I want my money back.