Blazen, Just because you don't think it's wrong, doesn't mean you aren't wrong.
Think about it this way:
-He payed for the acct... it's his, banned or unbanned it is still his.
-you say he "abandoned it" this is your only defense, and it's a bad one. You have no way of knowing whether he abandoned it, or was just letting it sit there.
-More or less, you have no right to that acct. Although he may have got it banned, it is still his account, and by taking it back, you ARE stealing.
Final analogy:
Think of your self on a highway, your driving down the road and you see a truck you just sold a few days ago. You look around and don't see the owner anywhere. You look and the only thing wrong with it is that it's out of gas, so you take some gas out of your truck, fill it up, use your spare key, and drive away... Although you still had the key, and fixed the truck, doesn't mean you have ANY right to that truck.