Erroneous Late pay fees

i have been disputing late pay fees with nextcard headquartered in phoenix. I disputed aseveral charges in that I had paid off my balances and mailed in remittance 10 days prior to due date in both instances. They only reversed one payment fee, I continued to dispute via internet and letter, i also cut up my card and sent it in. They not only continued billing me the disputed late pay fee but charged me additinal late pay fees on the late pay fee I disputed plus interest..the balance is snowballing. I have paid infull all balances owed prior to due date and thety are suffoacating me with late pay fees on late pay fees.
what rights do i have?
I am a Illinois resident

Do they have an #800 number you can call?

Since this is a dispute with the creditor (and not a 3rd party 'collector'), the FDCPA (Fair Debt Collections Practices Act) does not apply.

However, there is a law that gives you certain rights against the creditor, called the FCBA (Fair Credit Billing Act). To read the rights that this Act gives, click on the following:
http://www.ftc.gov/bcp/conline/pubs/credit/fcb.htm

You will see that you can demand in writing that they explain IN DETAIL any and all posts made to your account.