Turkish Airlines Return Ticket Cancellation Issue

A few months ago, I purchased a ticket to fly to Istanbul in August. However, I later decided to fly earlier. Before canceling my original ticket, I contacted Turkish Airlines and asked if my return ticket would be affected if I canceled my original departure ticket. They assured me that only my departure ticket would be canceled and that my return ticket would remain valid. Based on this information, I bought a new departure ticket and flew to Istanbul. When I tried to return to Germany, I was told that my return ticket was canceled because I did not use the original departure ticket. As a result, I had to buy a new return ticket, which I believe is unfair. I would like to get a refund for the amount I paid. Emriye d**.

Canceled Ticket Number: 2359240579287. New Ticket Number: 2352199691458. The person who assisted me was Mr. c** o**. Office number 4. I paid 412₺ for the new return ticket.