Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Sorry to hear that you are experiencing issues with this situation. Could you please sign in to the following link using the same email address that has the active subscription?
https://account.microsoft.com/services
Once you are signed in, select the option to manage the subscription and then try to change the payment method.
If you are unable to complete the process, please share a screenshot of what you see (without including any personal information).
If you cannot manage the subscription from that link, it is possible that the subscription was originally purchased through a third-party store rather than directly from Microsoft.