Military loan gone bad!!!! HELP PLEASE!!!! NEW BABY AND ALL!!!!

I received a loan in 2006 this was my 2nd or 3rd loan with this company I made payments and when I called to set up an allotment I was told this loan was paid in full, now as of last week Oct 2008 I was informed I owe money to this company and they refuse to answer why they told me it was paid in full. I do not have the banking data as I changed accounts so I am unsure what to do. This was a written contract, so as you stated Nevada is 6 years. Yet it was never placed on my credit report, and no one had said anything for 2 years? Then is it still valid?