… for example, my Target credit card … it’s due on the 20th. My bill “cycles” or whatever on the 26th (that’s when Target takes the interest I owe them out of the balance on the card …) so if I pay them extra on the 22nd, it just goes to the BIG balance and I still have to pay for the next month. If I pay them on the 28th, whatever I pay them goes toward the next month’s payment … ya dig?

You gotta find out when your “cycle” date is …

Simply put, you will not have to pay in Sept.
But, it is better to still make a payment just to get your balance lower, you do not want to carry more then 30% of your line of credit. Go above the 30% debt utilization and your score starts downwards.

I have made double payments many times and when the next month statement arrives it has always shown a payment due of $0 for the month.

Since you already paid for August you can wait til after your August due date and anything paid after that due cycle will be applied to your September Bill. Otherwise, it will continue to simply be applied to your August total.

So if your closing date is September 1 and your payment is due September 16 and you make a payment that clears on August 28 you would still owe a minimum payment by September 16.