wrong collection charges

Hi,
I recently received a bill from a collection agency stating that I owe $6000 to a private university in NJ. 5 years ago I took an online summer course there, after that my work schedule did not permit me to take any other courses. So, I informed them about my situation. For the last couple of years, I have been doing part-time studies at a different public university. Now, I received this bill from collection for 2 courses that I never registered for at that private university. It seems like there is a mistake on University's end about this bill. They claim that they have sent me mails on my old address, which I never received. What legal options do I have available to clear myself from this situation and protect my credit record?
Thank you very much.

Regards,
-FA

The letter should say somewhere on it ---something like "This debt will be considered valid unless you dispute in writing" yada yada yada.

Send them a registered letter asking them to verify the debt, stating that you dispute the validity of the debt. At that point, they will be required to contact the school and ask for your records to prove the debt is valid. You should also ask for those records from the school if you have not received them yet. Have you simply called the school and called their attention to this error?

I contacted my school today via email and they sent me, within hours, a copy of my financial record ( pdf file).

You may want to refer to this thread for more information: Fraudulant Student Loans.....HELP