cach llc CACV Fee on top of fees Denver, Colorado

I had a credit card with Providian with a balance of $500.00. I called Providian and made an arrangement to pay off the card $50.00 a month, the minimum payment was $35.00. I was going to be traveling.
When I called to close my account a year later, I found out I was charged a membership fee and late fees and my balance after a year was $800.00. I spent a year of sending them $50.00 a month, or $600.00 and still owed more than the orginal purchase. They, WAMU, would not settle.  Than the account was sold to CACH LLC with a balance of $1620.00. My good name is at stake. How do I get this resolved?
Cach llc  # 151101810810