Loan on Lending Firm Using ATM

In 2007 or 2006 I got a loan from a lending firm using my ATM where they would collect my payment monthly. My loan amount is 7,000.00. but after sometimes I was laid off from my work, and can no longer pay the remaining sum but I'm willing to pay them partially. But because I didn't find a job for sometimes i begin to not being able to pay my obligations. Now after some years they come to my house showing me a letter that I have to pay 24,000.00 including interest.. What can you advice me this is almost 4x my principle loan. I am willing to pay cause it is my obligation but isn't the interest so high. and I am afraid that even if I pay they will still charge monthly interest for my remaining balance. What can I possible must do?, please give me some advice. They even told me that a sheriff is going to come in my house.

do you even have a written loan agreement? what is the rate of interest and penalty? make a computation if their claim is correct