I don't really understand. You were paying for the dyno, but they deleted your instance anyway?
On Heroku, databases and dynos are completely distinct entities, each with their own payment plans.
When you set up a dyno and “add” a database, as most people do, it’s really easy to think that they are part of the same plan, and conclude that the “pro” or paid dyno is actually the combo of the dyno and database. They are not.
I understand why they did this, databases can be shared between applications, that’s handy, but this is a sharp edge.
This gets people on the phone with support quickly if they don't react to their account manager or mails. Like, we've had a possible security incident coming from a customer system and they didn't react - because they tried to hide their processes internally. Scream-Testing got us on calls with their InfoSec in a hurry.