Pegasus Airlines Denied My Boarding Due to a Fully Booked Plane

I bought a ticket for the Antalya-Istanbul-Erzurum flight, but they kept me waiting at the ticket checkpoint, they said the plane was full, I was told we could send it on a different flight, but I suffered a loss because I was late for my meeting. They said they would pick me up if anyone didn't get on the plane. It was really a disgrace. Why were tickets sold for the full plane and why was this informed at the gate at the last minute? I hope they are aware of my loss.