Turkcell Is Charging Me ₺13.90 Monthly to Fix Call Forwarding Issue I Can't Disable

My Turkcell line has been giving me a lot of trouble for a while now. Whenever someone attempts to contact me when I am currently on the phone, their call is automatically directed to a busy tone. Unfortunately, I have no idea whether I have missed a call because I do not receive any texts or notifications informing me that I was contacted. I couldn't remove the number 0539757**** from my call forwarding settings after examining them. "Your operator does not allow this action." is the error message I receive every time I attempt to delete it. In addition, I was asked to sign a contract for an extra ₺13.90 monthly price when I attempted to disable call forwarding using the Turkcell app! Fixing something that is obviously not my fault shouldn't cost me anything. I would like this matter to be addressed promptly.