Overcharged

I entered the Sandton station yesterday afternoon at about 3:30pm with my dad. It was his first time on the gautrain and so i was going to show him how to get to the airport. We entered and promptly arrived at the airport. He checked out of the airport and i remained in the train to go back to sandton station.I arrived about 45min later. I couldnt check out of sandton station as i had entered there, fair enough. when i queried this at the teller, the teller asked me where i went, i told them the airport. They said i should have checked out there, but i said i wasnt planning to get out there. So i asked if they had a window period of checking in to checking out (where customers are charged a nominal fee), they said they have never had it. So i then asked if i could just go to rosebank station, check out there and come back to Sandton (so i pay lower fee), the teller responded 'no'. I then asked if i could pay a cancellation fee of sorts. The teller would not offer me an alternative. She then proceeded to charge me a return ticket from the airport.I think this was extremely unfair, considering i never got off at the airport. Why is there no window period for possible cancellations?