If you actually have email responses from them, you might have a sufficient paper trail to make it worth trying. That said, assuming you only provided an idea and discussion, you probably don't have any particularly strong IP claim over their independently developed game even if you can show that they got the idea from you. So, it really depends on what result you want here. You probably won't manage to get any money out of them, but you might manage to get them to add a credit pointing at you.
