Discovery card has ****** my money

I have been a card holder for 2-3 years. I spend R50-R100k pm. I pay my balance to R0 3-4 times per month. I have never paid a cent in interest - until last month.<br> <br> I was charged over R400 in interested. I sent an email asking why this happened given that:<br> - I always pay my balance down (usually 3-4 times per month actually!)<br> - I have 55 interest free days<br> - I never draw cash (which I know is charged interest from day 1)<br> <br> In response I was sent a completely unhelpful document with transactions going back from Nov to Jan (when I know I did pay off my balance). Im a business analysis as a profession (and have actually work as an analyst for a credit card company) and I couldn't understand that document. Which means that basically that your average person certainly wont understand it - which means its pointless.<br> <br> In short, I want to know why, given that I pay my balance each month (3-4 times per month) I was charged this astronomical amount of interest.<br> <br> If you cannot answer this question for me then I want you to please shut down my account. I will rather take my business (which Im sure makes you a lot of money) elsewhere