Sends past statements at present

Dear FNB I just received a statement on the 27h May 2015 to make payment on the 18th May 2015 but I just made another payment on the 26th May 2015. Last month the same thing happend where you sent me an sms to pay R3k and I did and only to receive a call from Samantha to say my account is outstanding and I need to pay R5k, I didnt understand how but I made payment anyway and this month the same thing happens again where now I no longer even receive SMS's of the amount to pay and the due date. And also when I check on the 25th May 2015 you charged interest so many times on the same day and its different amounts? This is my first time doing business with you with a credit card and it has become extremely frustrating, dont you people know what you are doing? How many instalments does one pay in a month?