Who should i file a law suit against?

I have been receiving a call from a collection agency alleging that i am owing an hospital money, Problem is my insurance company has settled it with the hospital and they have even giving me proof that they have settled this. I have forwarded this proof to the collection agency and told them to confirm this with the hospital for some strange reason a different person from the Collection agency keeps calling , and they keep acting like they never got the proof, I intend to file a law suit against one company if any thing happens to my credit. I am not sure which one . The hospital or the collection agency

You are WAY ahead of yourself. Read this http://www.fair-debt-collection.com/

maybe you should send the proof to the hospital, afterall they are the ones that hired the collection company.

the agency...........

If you file a lawsuit, name both the hospital and the collection agency as defendants. That way, you won't be stuck if they blame it on each other. (And they probably will.)
That way, if the hospital says that it's the agency's mistake, and the agency says it's the hospital's mistake, they will have to work it out amongst each other and you win either way.
Though collection agencies usually ask for proof if you dispute that you owe a debt, and your proof should have been enough to get them to leave you alone.

file a law suit with bill gates... he has a lot of money for you to take..

First of all the next time they call ask to speak to a supervisor, keep your cool, don't answer any questions, just keep insisting you want a supervisor. Then tell the supervisor that you will file a harrassment suit if they don't stop calling you as your insurance co has taken care of this and you've already sent them proof, take his/her name as soon as they come on the line.. let them know you are taking their name. If they ask for proof tell them you will send it one more time to their attention, and if you receive one more call you will file immediately and they will be named. It worked for me. Good luck.