Turkish Airlines Ticketing Issue

In February, I purchased 4 tickets for my family through Turkish Airlines for a flight on April 13, 2024, scheduled at 16:50/18:35. My wife and children were assigned seats 10ABC, and I paid for a seat across the aisle. Later, I received an email stating that my flight had been transferred to another jet. On the day of the flight, when I went to check-in, I found out that my seat had been changed to the very back of the plane. Instead of traveling with my wife and children, I had to sit between two strangers. I filled out a feedback form on the company's website to address my issue. Nine days later, I received a reply asking for my ticket information, which I had already provided in my initial complaint. When I tried to resend the information through the provided link, I couldn't because the company had already responded. I attempted to submit a new feedback form, but the system kept logging me out. It's disappointing that a well-established company like Turkish Airlines doesn't have a direct phone line for customer service.