Turkish Airlines Ajet Flight Transfer Issue

I purchased an international ticket from the Turkish Airlines website. Since I was traveling with a child, I bought the premium package that includes seat selection and chose our seats. The flight was supposed to be an Anadolu Jet flight, but it was later transferred to Ajet, and now my selected seats are no longer available. I can't select seats anymore. I paid extra, and now my chosen seats are gone. When I call Ajet, there's a 40-minute wait time, and when I finally get through, they tell me to resolve the issue with Turkish Airlines since the ticket was purchased from them. When I contact Turkish Airlines, they say it's an Ajet flight and they can't handle additional services. They even mockingly suggest that I can get help with seat selection at the airport. Obviously, we can't travel standing up. I took precautions and booked my flight early, paid extra for the premium package, and selected seats because I was traveling with a child. They take the extra package fee and then take away my rights. I've submitted feedback through both channels, but no one has responded. They provide no solutions. It's a shame what has become of this prestigious brand.