Why did I buy a more expensive ticket than the one currently displayed?

You have visualized a more attractive fare than the one obtained when you booked... We understand your disappointment but it is common that the fares differ according to supply and demand.
The objective of an airline is to ensure the filling of its aircraft and, depending on the reservation fare, to adjust its fares according to demand.
In your case, our prices were obviously regulated because the supply of seats still available was higher than our sales targets.