Turkish Airlines Downgraded My Upgraded Flight

I purchased flight tickets for two people for the routes Istanbul - Barcelona and Barcelona - Istanbul between October 12th and October 15th, 2023, from our national and domestic airline, Turkish Airlines. We decided to upgrade our tickets to business class by redeeming 60,000 miles. Approximately 20-25 days later, I received a notification on the mobile application informing me about a tariff change. The message stated that I could either cancel/change my ticket free of charge or confirm the new flight details if I still wished to fly. We chose to confirm our flight. However, upon clicking the confirmation button, a new ticket was issued, and to my dismay, we were downgraded to economy class once again. I subsequently had several conversations with customer representatives, requesting that my ticket be upgraded again. Unfortunately, my upgrade right, which was canceled due to an error in their own application, was not reinstated. I was informed that there was no availability in the upgraded class (J class) and that this was in line with the airline's rules and practices. It appears that the free upgrade rights offered through the Miles & Miles program are being used sparingly, and passengers are being deprived of their rightfully earned upgrade privileges when accepting changes under the guise of tariff modifications. I am sharing this complaint to bring awareness to the treatment of Turkish Airlines passengers.