Driver charged for a cancellation

So called for and Uber, then realized that he was stuck in traffic and I was running late. I canceled the trip, but the driver still charged me. What angers me is that I was qualifying for a 30% discount on trip. I was supposed to pay R18 but the driver charged R40. He is a ***** and I’m very angry. I’m now going to use taxify as this is not the first time thus happens. Complaining on the Uber site is useless as they do nothing.