maxverse parent
Is there any reason to not just privately email the users? "Hey, I'm so and so, a security researcher. I was able to gather your data from <Company>, which has not responded to any inquiries from me. Please be aware that your data is mismanaged and vulnerable, and I encourage you to voice your concern directly to <Company>."
Seems like a reasonable idea, though depending on how many users are affected that may effectively amount to going public. Also only works if the vulnerability gives you access to all customer emails, and you're willing to exploit it to get that info (which might not be a good idea legally speaking).
Make it better: find a lawyer that would sue, send them the details, you can find like 10 ppl out of 10k who would love to sue, you get your bounty from the lawyer.