Legal Advice: who owns rights of personal Heroku account?

I need a quick legal advise. I'm in a situation where I was fired by a company but within a few days after they're threatening me with legal actions if I don't provide "company's property". By this they mean that I need to share my personal login info of a Heroku account that I had created while I was still employed there. That Heroku account just points to their Github account so they can run the server and view the app. Should I share my username and password with them if I don't want to?