Turkish Airlines Denied Me to Board Despite My Reasonable Excuse

I purchased a plane ticket easily and without any issues using my mobile device. I went to the airport with my fiancé, and we arrived at the gate where we were supposed to board the plane. Despite the scheduled time, the gate was still not open. When we asked about the situation, we were told 'soon.' Then I realized I didn't have my watch; it was left in the plastic tray at the security check. I immediately went back, signed some documents, and retrieved my watch. This took no more than 15 minutes. When I returned, the gate was closed, and a staff member told me it had closed 9 minutes ago, even though there was still time before the plane's departure. We asked the staff to open the gate, but they said they didn't have the authority to do so. Turkish Airlines is definitely over for me. I immediately found another flight and had to buy a new ticket at the highest price without any assistance. I do not forgive the airline company or those who use this brand.