Booking.com Refund Not Received After 3 Months for Canceled Edinburgh Apartment

I booked an apartment in Edinburgh through Booking.com on June 1, 2024, with free cancellation until the specified date. However, the apartment management charged my credit card the next day. On June 2, 2024, I canceled the reservation and emailed them, requesting a refund. They assured me that I would receive my money back within 15 business days, but it’s now been 3 months, and I still haven’t received the refund. I contacted Booking.com customer service, and while they promised to help, no progress has been made. I’m extremely frustrated and demand that my refund be processed immediately.