I am no lawyer but I believe its unlikely that you can do much.
- Does the date of international publication marry with the time period
of your presented solution?
- Did you have a contract or some other agreement that said your
designs were yours unless bought/paid for?
- Did you have a contract that protected your ideas for a period of time (unless protected via trademark/copyright/patent most contracts at least within the EU will only offer protection of up to six months, a year at most)?
I recall some years ago (more than ten?) a story on the BBC news site (which I have tried/failed to find). A couple had proposed a marketing idea to a well known confectionary/candy company and even sent a video of the concept/idea. The couple got a thanks, but no thanks and were told that the company were bound by contract with an external marketing company.
Some months later, an advert appeared on TV and in cinemas that was near identical of that produced by the couple. They challenged it and lost. I cannot remember the reason, but if you have not protected your idea (with copyright/patent/trademark), you could be successful, but it will be an up hill challenge.
Instead of beating them up, it might be worth considering trying to warm an otherwise cold relationship. If you have not dealt with them in three years, try approach them and see if you can get new work out of them. But if you feel bitter (and I say this with respect) its perhaps best not approach them as it could create more stress than its worth.