Turkish Airlines Changed My Seat Even Though They Were Paid Seats

On January 17th, Wednesday, I purchased tickets from THY for a flight to Trabzon. Additionally, I paid extra to ensure my 2.5-year-old son could sit by the window and I took the middle seat next to him to avoid any contact with others. This morning at 07:38, I woke up to messages and emails indicating that our seat numbers had been changed. They separated my son and me, placing us in different seats. When I called customer service, they repeatedly cited the reason as 'aircraft type changed.' For the past 8 years, I have traveled to and from Trabzon at least 3-4 times a year, and the aircraft has always had a 3+3 seating arrangement. What does 'aircraft type changed' mean? Did it change from 3+3 to 4+4 seating? Did it go from a single aisle to a double aisle? What kind of change would necessitate altering our seat numbers? If the aircraft still has a 3+3 single aisle arrangement, the window and middle seats should not change. If I paid to choose our seats, they should not be changed. You cannot separate me from my 2.5-year-old son; we must be seated together. If you cannot issue a ticket to a child under 11 without a parent, then you cannot separate them from the parent. If I wanted to sit separately from my son, I would not have paid for specific seats; I would have accepted whatever seats the system assigned us. As usual, customer service listened and asked me to submit feedback online. I did, called again, and was told they would get back to me. While they quickly make changes without my consent, urgent corrections are delayed. THY consistently prolongs problem resolution without offering solutions. I have faced seat change issues before, right before boarding, with the same excuse 'aircraft type changed.' Once, only my seat was changed, and a gentleman approached me on the plane saying they swapped my seat to sit with his wife. Can such a thing happen? On another occasion, on the return flight from Trabzon, our seats were changed again, and after much argument at the gate, we were given window and middle seats again. Saying 'you approved the procedures while selecting seats' is a ridiculous response. It does not say you can separate a mother and her 2.5-year-old child. It does not say you can move a paid window seat to an aisle seat and send us on the same aircraft type. I urgently expect a solution.