Sorry for the confusion, and thanks for pointing this out — we understand how this can be misleading.
The information shown on the website is not fully up to date.
All purchased credits (including monthly, yearly, or pay-as-you-go) are valid for 6 months from the date they are added to your account. They are not limited to just the current month.
For the Yearly Plan, it means you are billed once per year (at a discounted price), and credits are issued monthly to your account. This is designed for long-term users.
Regarding your case (credits not showing for the new month), that is not expected. Please try refreshing your account or logging out/in. If the credits still haven’t appeared, we recommend contacting support or sharing your account info so we can check it for you.