It is correct that your premium plan was automatically downgraded on 22nd September. As premium is a month in advanced, your payment history shows the payment deducted from your earnings on the 4th September.
With the automatic downgrade will will calculate the days you payed the higher fee for premium and deduct this from your next invoice which will be due on 4th October 2023.
You can see this in your premium dashboard as well: https://premium.ezoic.com/premium/account
I hope this clarifies your questions.