Paid for seats but got separated

I flew from Indonesia to the U.S. with a layover in Istanbul. Each leg of the trip was 12 hrs. I was flying with my daughter and our cat.

First leg was great. We were in the seats I paid for and had the 3rd seat empty.

During our layover I realized our next flight, we were not in the seats I paid for and we were separated.

I went to customer service and was just told, “Flight is full, cannot change.” I reminded them I paid for the seats and he just said, “Tall to the gate agent, have a nice flight.”

Extremely rude.

Waited for a gate agent to arrive. And I got the same thing but then told to talk to the flight attendant.

Flight attendant basically had nothing for me but “Maybe someone will switch.” Never followed up.

Thankfully because I asked and we were trading aisle for aisle someone did trade with us but I’m so upset at the rudeness and lack of resolution and answers when I paid for the seats well in advance when I purchased the tickets.

Does anyone know why they would do this? Will they refund me for seat selection?