Diamond Preferred Citi Credit Card review: 29.9% Citi Card has charged me 2

I have been in a sales job and I have been on very crazy schedule for years. So
I did not check its interest. Last September I lost salary job since then I am on unstable commission job. I have used the Citi Credit Card for 5 years and since 2010 I began install payment of $300 every month so that I can keep up with its payment. This month I made $200 payment manually and call Citi to stop automatic $300/m payment . There is no bill payments are behind.My credit score is around 680 and not bad credit score.
I asked the customer service what interest rate they have charged me on the card. They told me 29.9 %, I was shocked and very angry.
For 2 yrs in order to pay off the credit card, I have paid $300 every month and I seldom used the card. Today I realized CITI has charged me 29.9% interest almost 30% and learned that is why it seems I am not able to pay down any principle.
I asked Citi to lower interest but they are not willing to do it and only Citi offered me is giving me 7.99 % for new purchase. They would still charge me almost 30% on existing balance. I also asked whether they can lower the amount of balance I owe because I having a financial hardship and 30% interest is not justifiable but they refused to do it. Citi Credit company has been taking advantages on me. I need strong supports to stop Citi credit company taking advantage on me further.