My loan was forgiven in 2004 but as of 2009 Sallie Mae said it was forgiven by mistake.

Yes, you should take the time to meet with an experienced bankruptcy attorney that handles chapter 7 and chapter 13 cases and is willing to handle litigation within the bankruptcy filing. Most bankruptcy attorneys will meet with you at no charge for the initial appointment. You can use the "Find a Lawyer" link at the top of this page to search for an attorney. Although it is very difficult to discharge student loans in bankruptcy, our firm has been successful in establishing that our client did not owe a student loan because he did not sign the guaranty of another persons student loan as the signature was forged. We have also been successful in establishing that all or a portion of the debt was not for a educational benefit and was dischargeable. The question to whether the fact that the debt can be reinstated after notice that the debt was forgiven is an interesting one. I do not know the answer to that question, but you should contact an experienced bankruptcy attorney to get that answer.

Do you have something in writing from Sallie Mae that the loan was forgiven by accident? If not, I think you may have a decent claim against Sallie Mae for conversion (taking something from you that it is not entitled to) or unlawful debt collection. On the other hand, if one loan was forgiven and another loan was not, then it is entirely possible that you are still responsible for this other, second loan. (I'm not sure if I understood the facts leading up to your question regarding the other loan.) I would suggest you talk to an experienced consumer rights litigator.