I'm Marco and I work in the ops team at Nexmo. I have found your initial email to our Support team, and I can see that there have been some changes in our dashboard related to your report. I am not sure it's fixed because I don't have the details about the vulnerability you discovered, but I do know that initially we were resetting the user password straight away after a request. This is no longer the case - the email address now receives a reset link. If your report is still relevant despite this new procedure, I am very happy to receive the details.
Also, I would like to respond to the complaints that "we don't care about security". This is simply not true and we even use a bug bounty reward program. We do care and we accept reports through https://cobalt.io/ (ex CrowdCurity), so if you share with us your username/email on cobalt, we can add you to our program.
I totally agree we fucked up handling your report better back in may. I hope you are still willing to work with us!