@ben you gave them information for free. You don't own it, they do. That was the working relationship.
Imagine if you were working for a company producing work and you suddenly tried to sabotage that work. That's what you were trying to do, sabotage it. They would be perfectly within their rights to restrict your access.
The moral of this story is, if you want to retain ownership then don't give it away (for free) to someone else.