Turkish Airlines $250 Preferred Seat Downgrade and Refund Denial

I am writing regarding my Turkish Airlines flight TK30 from Newark to Istanbul on 17/10/26, for which I purchased a preferred seat during the booking process. The seat I selected was advertised as being wider and having more leg room, and I paid an extra $250 specifically for this preferred window aisle seat. However, just hours before my flight, I received a message from the airline informing me that I had been moved to a different seat. The new seat was not a preferred seat and was not the window aisle seat I had paid for. I was told this new seat was an “equal” extra leg room seat, but on your own website this type of seat is listed at around $150, which is clearly cheaper than the seat I originally purchased. Before boarding, I spoke with the agents at the gate about this issue and they explained that the aircraft had been changed and the replacement plane did not have preferred seats. I made it clear that I did not pay $250 just to end up in a regular aisle-type seat, and I asked at least to be placed in a standard seat and for the extra amount to be handled properly. I was told there was nothing they could do at that moment and that I should contact customer service after landing to request a refund. After the flight, I called Turkish Airlines customer service and was directed to fill out an online form about this issue. Two days later, I received a response stating that I had already been compensated by being given an “equal” extra leg room seat and that no refund would be provided, which I do not accept because the original preferred seat I paid $250 for was more expensive and different from the one I was given. Since I did not receive the preferred seat and service that I paid the $250 for, I request a full refund of the $250 seat fee. I ask that this refund be processed as soon as possible and that a clear explanation be provided as to why I was downgraded to a lower-priced seat without my consent and why my refund request was rejected.