I would go back to that house, speak with an adult and request that paperwork. I then would cancel that credit card, and get a new one issued to you.

The fact that they opened your package and have paperwork that may have compromising personal information when it was clearly addressed to you, in both name and address, is fully against the law and could be quite a persuading argument if they don't fork over what is yours.

Perhaps a better way to go forward in the future would be to have packages delivered to your nosy retired neighbor's address, having it signed upon delivery.