Hello, this is Emily.
You can paste the screenshot in your reply and hopefully that works.
Without seeing the exact notification, I might be giving you the wrong answer, but based on what you described, it can be a cache issue.
Go to Settings > Accounts > Access Work or School, click on your school account and disconnect. Restart the computer. When you use Office 365, sign in again and see if that clears it.
Another way to try is to go to Control Panel > Credential Manager > Windows Credential. Find all mentioning of old and new school accounts, delete them. Restart and sign back into Office 365 to see if it works.
If neither works, once I see the screenshot, hopefully I will have a better idea what's going on. Thanks!