Turkcell Added a Yearly Contract Without My Consent and Demands a Termination Fee

I was attempting to buy an extra package from Turkcell Mobile when I accidentally ended up with a yearly postpaid contract on my account. Upon reaching out to customer service for cancellation, I was told that a termination fee of ₺4,000 would be added to my bill. This situation is completely unacceptable, as I did not intentionally activate the contract. I would like to cancel this agreement without incurring any penalties, please. I have always been a dedicated customer and was surprised to face this kind of problem. If this issue isn't resolved, I will have to consider taking legal action to address it. I trust that Turkcell will address this issue appropriately.