I want to sue my credit card compan

I have 2 accounts with Retail Services which I have had for 15 years. The
accounts used to be on another company with an interest rate of 15.9% They were eventually bought out by the criminal Retail Services which originally called itself Household Retail Services but they changed to Retail Services due to all the bad stuff that people reported on their business practices. Once they became my creditor, my interest rate was immediately changed to 20.9%. I was outraged but couldn't do anything about it because I had signed the original agreement which as you know says they can do whatever the hell they want after the fact. I owe almost 16,000.00 and have maintained a perfect payment history and my credit report was without blemish........20 years of perfect credit. I recently lost my job due to the closing of the company after 18 years, and have been struggling to make payments. I called them and told them I would be paying late and I did so 2 weeks late. They were nice about it, and the following month I paid them 2 days late, that's when all HELL broke loose. They changed my interest rate to 24.9% and refused to lower it. That means that I am now going to be paying them almost 60.00 more per month that will not go toward my principal. I have refused to make another payment until they put my interest rate back to their already criminal rating of 20.9%, they of course screwed me by damaging my credit irreperably. Is it OK for them to rob me by charging more interest and then destroying my credit as a bargaining chip to force me to pay a higher interest rate. I mean I never missed a payment EVER in 15 years. I want to sue them for unfair business practices and defamation, can I do this? and do people win in these situations ? Thank you for your help