It's pretty obvious that when you find a flaw you simply don't approach the people responsible for it, unless they have an EXCELLENT reputation of dealing with this. Otherwise do an anonymous full disclosure (edit: if you have an entity that routinely handles this sort of thing and has an EXCELLENT reputation, that would work too). If nothing happens, provide a PoC.
Of course people, even in IT, are kind of weird here. Somehow responsible disclosure got into people's minds as The Good And Proper Thing to do, and full disclosure being somehow irresponsible. Analogy: Some guy finds out the mayor is completely corrupt or does some illegal stuff. What do you do? a) Disclose this through e.g. the press b) Approach the mayor and try to get him to fix his stuff. Somehow, when it comes to IT security, people wanna see hackers do b) because a) would clearly be irresponsible. Wtf?