Virgin Active South Africa
Booked spinning bike given to someone else

I booked for the 5:30PM spinning class online, a week before the class.
I arrived at the class at 5:28PM to find that the staff had given my bike to someone who had not booked.
On enquiring, I was told that if I'm not at the gym at 5:25PM (5 minutes before the class_ that the bike is given to someone who hasn't booked.
There is no signage or such a rule documented anywhere.
Surely you can only give away my booking if I'm late for a class?