[zefix]

If it is a larger-profile German or European webpage, contacting c't / heise investigativ would probably be a good idea.

They are the largest German computer magazine, and have a great track record in getting companies to change bad practices and respecting consumer rights. I also consider them trustworthy w.r.t. not inadvertently leaking the problem.

They have a secure contact form under https://www.heise.de/investigativ/