What Are My Legal Remedies If A Hospital Thinks I Owe Them When I Do Not?

In 2002, my wife received services from a hospital. These services were covered by my insurance provider. The hospital incorrectly (their fault) claimed the wrong provider. Finally, they did claim the correct provider but did not submit the correct form required do the the length of time between services performed and the claim. I received many letters from different collection agencies and explained this to them. In 2007 I sent a letter to the hospital and copied the current collection agency. In the letter I included copies of documents from my insurance provider that proved the hospital did not fill out the correct forms and the documents stated that the insured (me) was not responsible for reimbursement to the hospital. I have now received another letter from a collection agency for this. What are my legal rights? I am tired of trying to fix this. Can I bring legal action against the hospital? If so, what type of action? Can I sue for reimbursement of legal fees?