paying off debt

I will be paying off a debt to an attorny's office.(janovivh&Block).Tey told me a few months that I will also owe a 6% interst fee also,plus courts costs.I was making making payments before they got involed and they sued so I counter sued.They called right away and just wanted me to make payments to them.I thought I read somewhere that a debt collector cannot add more interest then the orginal debt and that any fee's are to be paid by the collection agency.Also I feel that since I paid the court fee's to counter sue it should offset there fee.