- Create subscription for one year → Money was charged, I have subscription for one year.
- Cancel subscription → I still have subscription for remaining period of my subscription.
- Create subscription for one month → Money was charged again. Now I have paid for 1 year + 1 month, but have only one month of paid subscription.
When you get money from your customers you need to extend paid period, but not create a new one from now.
Actually you don’t need to charge money if current period doesn’t finish yet.