registration id

Good day. My registration code was acquired without permission by my brother, how to I discontinue him from using it nor from sharing it?

So, I recently bought a bundle for iOS, and I shared it with a friend, and then tried to share the code with my sister. When I shared it with her - the message said I had used that ID too recently, and that someone can override it. Is there a limit to registration ID’s being shared? Thanks...