SunExpress Airlines Refused to Refund Cat Travel Fee

I purchased an extra service from SunExpress Airlines to bring my cat along with me, but due to a documented issue confirmed by the vet, my cat is unable to travel. I contacted customer service to request a refund for the cat extra, but I was informed that a refund is not possible. This response is unacceptable, and I cannot understand why a refund would be denied in such a clear and valid situation. I will be raising this issue on every possible platform until it is resolved. My PNR is TAEFKU.