Fast Cash USA ACS Threatening to seek legal action for charges such as fraud Internet

I received a phone call from a person at this ACS, stating he was an attorney representing Fast Cash USA named Arnold Watson, claiming I had a large outstanding balance with them after I made a "settlement" payment to them in Sept. 2009.
My arrangements were made with a Bryan Smith, and conversations with several other broken English speaking people at that time.  I called them to find out what my payoff balance would be and was given an amount that on their faxed paperwork as the fee that would "settle the account". Even though the principle balance plus heavy interest had been previously paid, I reluctantly paid the "settlement" to get rid of the nuisance.
Now 6 months later they are calling to inform me that this did not "close" the account, simply made a temporary settlement, and I owe them a large balance. 
I have not paid them any more, and expect they will continue the harassment with threats of fraud and any other intimidating tactic they can employ.
When you take out these loans they ask for a high interest rate, but fail to explain that in addition to interest, they institute a high "installment fee" which makes their profit soar.
I intend to file a complaint with the Consumer Protection Agency and local enforcement agencies.