Disgusted by SAA overbooking

I regularly fly on SAA and often travel on business class with my family. After today I will rethink this. They overbook their flights and couldn't care less about the people they affect. I arrived 1.5 hours early to check in to a domestic flight only to be told they had to put me on a later flight because the flight was full. This is after waiting for 20minutes for a seat. When i asked to speak to a manager i waited another 15 minutes and no one showed up so i left. They dont offer any compensation for what is their own fault. These types of practices are disgusting and UNACCEPTABLE. SAA's don't care attitude will end up costing them a lot.