Ask HN: What to do when a vendor doesn't respond to security issues?

I got fed up with a certain internet-connected appliance at home, and decided to investigate its firmware. Since the vendor claims the product is still in active support and not EOL, my main goal was to find a pre-existing CVE it was vulnerable to and report that so the vendor would need to release an updated firmware, hopefully with other improvements too.

The latest build was years old, so that wasn't too hard. I found an outdated service that is reachable unauthenticated from LAN and has a known vulnerability that allows arbitrary file reads on the device. I also found another endpoint that is unauthenticated from LAN and with a single GET request essentially bricks the device, requiring disassembly and JTAG access to recover from. There are no cross-origin checks or restrictions of any kind, so a malicious site could put the URL in an img tag or similar and brick visitors' devices with no interaction.

I'm in the EU, so I went to their EU site where I was first instructed to create a ticket on their support site. I tried numerous times but it always failed with "an unknown error", instructing me to "contact the service desk" with no clues how to reach them. I also found another form where you could select security issue as the topic, but the description field was barely long enough to fit "I found security issues with ${product}, please contact me for more details." Three weeks later I'm still waiting.

Next I filed the same security issue form on their US site, and promptly got a reply. The exact model isn't sold in the US so they wouldn't handle it directly, but promised to forward any details to their EU counterpart since I had such a hard time reaching them directly. I sent the issue details and have not heard back since. I sent a follow-up email asking for a status update, but so far that has gone unanswered too.

What should I do next? Is there some EU entity that could step in? Can I get in trouble if I just publish what I found?