Hey again!
Thanks for the information - does any old company profiles still exist? If so, can you gain access to those profiles to shut them down, update, or delete them?
What could be happening is that those profile URLs could be redirecting and somehow signaling that that company name is still associated.
Or, there may be some tagging in your code on your site that is referencing the old company and somehow translating to the Knowledge Graph.
Lastly, I would check your local SEO and citations to see if listings still have references to that URL and company. You can let these services know "Hey, this is ______ now and not _____ company." You can run your business through the Moz Local Check Listing and see what they find too.
Let me know if I can be of any more service! Good luck!