Talk to your advisor. If you have compelling evidence they may be willing to stake their reputation and research collaboration with this group in order to get them to at least acknowledge your contribution after the fact. Again, you need to be prepared to hear that your advisor will be very limited in what they can do apart from trying to straighten things out informally. Given that papers usually take several months to write, I’m curious to know why no one knew about this happening. 

Ownership of the idea is going to be hard to argue at this point given that the paper has already been published (and has won an award!). It won’t be withdrawn, it probably can’t be withdrawn since it’s already been published, not a reversible action in most cases. The authors could say that you misunderstood, that they independently came up with the idea, or any number of plausible sounding defenses.

Your best plan forward is perhaps to be involved in follow up work, and be more careful with this group who’s acted in an unethical and mean way.