Turkish Airlines Seat Assignment Issue on London-Istanbul Flight

Despite having chosen and confirmed my seat days in advance for my London-Istanbul flight with Turkish Airlines on 05.01.2024, I learned 12 hours before the flight that my seat was reassigned to someone else. After repeatedly calling the call center, I discovered that the seat I had reserved was sold to another passenger for a fee, and I was reassigned to a different seat. When I provided feedback and requested compensation, I received a demagogic response stating that the seat could be given to someone else due to disability/health reasons. Both the call center and the counter confirmed that my seat was actually sold for money to someone else. The issue here is that they sold the seat service included in the ticket price and took away my right if someone else paid more, without any explanation or communication. Due to this disrespect for passenger rights and disregard for human dignity, I must state that Turkish Airlines does not offer any service quality worth the price difference.