I have already paid in AppStore, but the realm still close

First of all, I have booked my realm a long time ago. I have paid for it each month,and it has no error appears. But for this month, when I pay 50 for realm, it reminds me to renew my realm, and I have to pay another 50?! Finally it shuts down my realm. There were money transactions evidence, so I hope you can figure out the problem thanks.