Ok, so let's start with not able to login with either user. If you can't login to SSH, the only other way to login to your Droplet is using console, which you'd access by clicking on the name of the droplet and then clicking on 'Access' and then 'Launch Console'.
To login to console, you'll need your
root user password. If you never received a password and your Droplet is setup with SSH Keys only, there's very little that can be done at this point, unfortunately, as you can't use SSH Keys to login to the console.
If you can login to console, you can re-enable
PasswordAuthentication by modifying:
and then restarting SSHD:
service sshd restart
You could then reset passwords using
passwd, such as:
Getting you back in is what's important right now. We can then work on setting up SSH Keys after though the best way to setup SSH Keys is actually to deploy them when you deploy your Droplet (as this makes it easier). You could then create a new user and we can walk through the setup,
If you can't login to console, short of submitting a support ticket and seeing if they can help get you back in, you would effectively be locked out and would need to deploy a new Droplet.
When you start tinkering with SSH and a Firewall, you have to be very careful.