I'm kind of confused.
Why did you sue your oil company? You said that you were being charged for a contract that didn't exist. Why not simply ignore the bills?
Why would you need a lawyer to defend you when you are the plaintiff?
The Fifth Amendment to the United States Constitution prohibits the government from making you answer any questions that may incriminate you.
Go watch this video. http://www.youtube.com/watch?v=6wXkI4t7nuc
Refusing to answer questions is NOT obstruction. Lying to the police is obstruction. If you say "I don't know" when you really do, that's obstruction. I suggest using the phrase "I'm sorry, but I don't believe it is in my best interest to answer your questions".