I've heard the term 'denied boarding' used for a variety of reasons so more details would be helpful. I think the VFA route is operated either by an SA Airways A319 (25J, 95Y) or an SA Airlink BAe146 which I guess has less seats. Overbooking either of those by 25pax (the tour group) plus your party would be a substantial overbooking in my experience. The route is only operated once a day so with limited alternative options, while frustrating, two meals plus hotel is probably as good as it gets.