Turkish Airlines Unjustly Charged a Fee

Hello, on September 28, 2023, I purchased online tickets from Turkish Airlines for my 77-year-old father and 75-year-old mother. Due to my father's age and hip problem, and my mother's knee problem, they have difficulty standing and walking for long periods. Therefore, I called 0850 360 3403 to request wheelchair service for their tickets. They asked for a fee of 44 € for this service. Despite stating that it should be free, they insisted on the charge. Since my parents couldn't walk, I paid the fee. Later, I found out that this service is actually free. I paid 1,550 ₺ for 44 € (they calculated the rate as 35.22 instead of 28.83). I feel... taken advantage of. I don't know where to file a complaint or what steps to take.