Overdue how?

I've had my credit card with you guys for +- 10 years now. Never missed an installment. Always paying . Installment R530 a month but I pay R1000. I pay end of every month. Yet every month usually any time from 25th of a month I get a email saying that my card is "Overdue" How can it be overdue? Do I only get till 25th to pay? I only get pay last day of every month and it's been like that for years. Do I not get to pay until or before 7th of the next month? If I then don't pay then it will be overdue. How can it be overdue on the 25th already? When you expecting money? I really feel like settling the card and just closing it.