Hello @Ijaz M
Thank you for reaching out. Azure AD Premium License Payment works little bit differently when compared to Azure Pay-As-You-Go Subscription. If your payment method on the account is expired or due for payment, then once the Azure AD Premium P2 license term expires, then Azure AD tenant automatically reverts back to free version if is being utilized by some other service. Complete details about this is mentioned on below article:
What happens to data when a subscription expires?
You should be able to manage payment methods for license-based subscription from Office Admin Center: https://admin.microsoft.com/.
You can also refer following Azure QnA post for more details Azure AD Premium License lifecycle: Delete Azure Active Directory Premium P2 trial
I hope this helps you.
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