When a flight is overbooked there is a system to determine boarding priority. I'm afraid that those traveling on award tickets are just one step above stand-by passengers and below all revenue travelers. The first priority would be full-fare passengers and through passengers. It's all in the fine print. The reason they didn't notify you is that they didn't know how many passengers were going to show up. It IS legal to overbook flights and your priority just wasn't high enough, sorry. But from what I can determine they handled it as would any other airline, according to the international rules of transport.
Mandi