Unfair Fees for Date Change on Pegasus Airlines Flight Tickets

I bought tickets for a flight from Pegasus Airlines. There was an error in my wife's birth date, and they asked for 550 TL just to fix it. I think this is an unfair profit for something as simple as changing the date. We couldn't cancel the ticket, though, because the fee for doing so was even higher. We only wanted to change a small part of the date, so charging us 550 TL seems like a lot. We want this fee to be refunded.