If your main concern is the shortness of the article, there are journals accepting also quite short papers, as Comptes Rendus Mathématiques or PAMS (Proceedings of the American Mathematical society), but they are quite selective, and what in your opinion is "a fundamental discovery" could be considered something obvious/unimportant/wrong by the mathematical community.
I have to be honest and say that, based on what you say, this seems most likely. However, it could well be that you found something relevant. There are a bunch of such cases in the history of math. So the right thing to do is to let your paper acquire visibility, while making it clear that it is your original work.
Luckily enough, there are resources for that. For instance, did you put your article on ArXiv or something like that?
This can let it have some visibility and, perhaps more importantly, can bring you some feedback.