Turkish Airlines Ticketing Trouble - Missing Seat for Second Passenger

I purchased a round-trip ticket for two from Istanbul to Paris for the dates of February 10, 2024 (departure) and February 17, 2024 (return) on August 10, 2023. During the booking process, I selected seats for both passengers, paying an additional fee. The chosen seats were 15A and 15B, and I made the payment using loyalty miles and the remainder with my credit card. Turkish Airlines (THY) promptly sent a confirmation email detailing the selected seats and payment after the purchase. However, a few months later, upon checking my reservation, I discovered that the system only processed the transaction for one person. Despite multiple feedback attempts to THY and providing the confirmation email, they consistently claimed that their system showed a transaction for only one passenger. Despite the confirmation email indicating separate seat numbers for two passengers and a payment for both, I received no explanation. I have been left in distress by THY, and no steps have been taken to address my grievance. Hence, I am filing a complaint against them.