Misleading and inefficient service from Car Trawler

When I arrived at Woodford Car Hire (OR Tambo) to collect my car, I learnt that my online booking had been made through a third party, Car Trawlers. I tried to amend my booking at OR Tambo to obtain comprehensive car insurance through Car Trawler, but was unable to do so. It is not disclosed on the website that one cannot amend one's booking with Woodford even though that is the company that I hired the car from. This is misleading.