FNB credit card June 2024 interest charges

I have been using FNB credit card for the past more than 5 years and below is how I have been using it without paying interest except with transactions that incur interest from date of use and they were paid accordingly. However end of June 2024 o was charged interest. When I ask on there secure chat I'm told that I have 30 days to use it and 25 days to pay. Some years ago I did ask credit card department when is the card cycle closed. It was mentioned on the the 29th of every month with an auto payment of the 25th of every month. In may I did transactions that incurred interest which was charged end of May and I did settle the credit card end of May as per statement that was send end of May FNB app. I did start new transactions for June and out of June transactions there isn't any transactions that incurred interest. I did pay the credit card on the 27th of June but to my surprise, I was charged interest. I have been using the credit card this way and I was not charged interest except on transactions that incur interest from their date.