Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
1
When you upgrade from a version of MIcrosoft 365 to another version with more functionality, then you will be charged the full amount for the new subscription, and the remaining days on the original subscription will be converted on a pro-rata basis to the new subscription.
CHeck the expiry date on your new subscription to check of you have more than 12 months on the new subscription.
2
Or if you are now being charged separately for two subscriptions, log into your MIcrosoft account on this link, do you see two separate subscriptions listed there, and if so, are you able to cancel the original subscription from there.