Issue with Turkish Airlines Ticket on Baku-Istanbul Flight

I purchased a round-trip Baku-Istanbul ticket from Turkish Airlines. Despite arriving half an hour before the departure of my outbound flight, I was not allowed to board. On the same day, I bought another outbound ticket from THY. When the return date approached, I called customer service to confirm if there were any issues with my ticket and was told there were none. I then purchased baggage worth around ₺2000. However, during check-in, I found out that my ticket was canceled. THY sold baggage for a canceled ticket! When I asked why the ticket was canceled, I was told it was because I didn't use the outbound ticket. Even if I missed the flight, I had bought another ticket from THY. Couldn't the authorized person in Baku make the necessary changes? If I had been informed that I might face issues with the return ticket and might need to pay a price difference, I would have agreed to pay. Upon arriving at the airport for my return flight, I discovered my ticket was canceled. I spent an hour talking to customer service (spoke to 5-6 people) trying to resolve the issue, but received only evasive answers. Finally, someone admitted that the person who sold the ticket should not have left it open and should have linked the tickets and applied the price difference, but then transferred me to someone else and disappeared. My approximate loss is ₺18,000. It's unacceptable for THY to sell baggage for a canceled ticket and employ incompetent staff in customer service or sales! This does not befit a brand representing our country worldwide like THY! I demand a refund for both the ticket and the extra baggage fee I paid!