Credit Card interest charged but I am NOT owing

Credit Card division

I used my credit card in Jul 2019 and then settled the entire amount I had used on 01 Aug 2019. This brought back the limit to its original form, the one that was granted on the card when I took it out. On 08 August, I received a statement with an opening balance of R20 215.27 and as such owe an interest of R536.13. From the original limit however, you have deducted this R536.13. Nowhere does this R20 215.27 balance show from the original limit I was given. What is this? This is the second time you want to ***** my money. In June, I paid the interest of +R200 yet I was not owing a cent when you drew your statement. Please explain - ***