Turkish Airlines Round-Trip Ticket Cancellation Issue

I purchased round-trip tickets from Turkish Airlines with the option to cancel both with a ₺525 fee. However, when I tried to cancel only the outbound ticket, I was informed that it was not possible and that both tickets had to be canceled together. They claimed that there was only one ticket number, so both would be canceled. If I bought two tickets, you should provide two ticket numbers. Why should we buy round-trip tickets if it causes such issues? We might as well buy one-way tickets for peace of mind. Is this system designed to charge us more? I paid a significant amount, and the refundable ticket only gives me ₺40 back. This is not fitting for your brand. I urgently request this issue to be resolved.