Dealings with NCO Financial?

I had a joint auto loan,co-owner defaulted,so I tried to take possession and honor debt...come to find out,dealer and co-owner altered title application after it was submitted for approval to lender...I am in possession of both documents,one with the lenders fax line on border,marking it as original,and one from motor vehicle dept,the result of a complete title history search,this one with my name removed.Obviously,I refused to pay for a vehicle I was never sold,and notified the lender,who according to equifax,has charged off to zero,and according to experian,the dealer has paid...neither report indicates a collection account,yet I have received calls from a NCO Financial,claiming to represent the lender,demanding payment.They have violated several FTC rules,including threats to call everyday,which they don't do,remarks about my(failed) relationship with the co-owner ,and refusal to provide validation of the debt,and legal advice that it is my responsibility to prefer criminal charges against dealer and recoup their money for them,and that I must sue the dealer ,as the outstanding debt is considered my damages,which it is not ,as I paid not one cent in real $$$...anyway,the debt is about to become time barred,3 years in Maryland,I suspect they are seeking acknowledgement of the debt to extend time.I have denied the contract was ever in force,as the vehicle was not sold as contracted.Any suggestions for finally ending this,maybe even getting a couple bucks for the aggravation?Damages would be hard to prove,as my credit score has recovered from this and currently resides over 800...