Booking.com Double Booking and Payment Issues

On June 16, I paid 4,680.93 TL through "Booking.com" for a reservation at Saklı Doğa Çiftlik Hayatı Taş Evi for June 20-22. When we arrived at the facility on June 20, they said the room was occupied and they weren't aware of the reservation. As a result, we couldn't stay there from June 20-22 and tried to contact Booking.com but received no response. On the same day, we found a new facility and paid 7,000 TL for a 2-night stay. On June 23, we attempted to contact Booking.com for a refund but got no response via their website message box or email. On June 24, we called their customer service number "00800 448 826 367". They said they would issue a refund and add the extra amount paid for the new facility if we provided an invoice. We requested and sent an invoice from the new facility to customer service, but they replied saying it wasn't valid because it didn't show a "0 balance" (indicating full payment). They asked for a 0 balance invoice, bank statement, or slip proving the 7,000 TL payment. We then got a stamped and signed letter from the facility confirming payment, which we shared with customer service. Booking.com rejected this too, saying the invoice should be in Euros. We have an invoice and a stamped, signed letter confirming payment, but Booking.com keeps making new demands, prolonging the process and abusing the situation. Since June 20, they've been unhelpful and have prolonged my inconvenience. They could have contacted the new facility directly but instead left the customer in the middle, continuing my difficulties. Due to Booking.com's error, I had to spend an additional 7,000 TL on top of the initial 4,680.93 TL. I'm requesting a refund for this difference.