Visa costs necessary

I have booked a flight for me and a friend from Johannesburg to Bangkok, flying Ethiad on Travelstart 2 days ago. They promote the flights as a sale for Etihad. We choose an option where on the return ticket it has a 21 hour layover. We do have no intention to visit Abu Dhabi and thought we will stay in the lounge for that period. Now Etihad informed me that I need a visa, which will be another R1000 plus for the flight. If you stay over for more than 8 hours you need a visa, regardless if you leave the airport building or not. I am asking myself why would Travelstart not inform one, when you purchase the ticket that there will be additional costs? I could perfectly understand if you want to visit Abu Dhabi, which is not the case here. We only bought tickets for a flight from Johannesburg to Bangkok. So the sale is not really a sale.