Hi gillianEdnie,
Thank you for choosing Microsoft community.
Based on your description, please first refer to @Stefan Blom's useful suggestion to see if it works.
Besides, I'd like to confirm with your about the subscription type - Microsoft 365 for Home or Microsoft 365 for Business. Check Compare All Microsoft 365 Plans (Formerly Office 365) - Microsoft Store.
A.
If you're using Microsoft 365 for Home (Family/Personal) and are using a Microsoft account, to change your Microsoft account from Gmail to Hotmail, please open an inPrivate browser window and refer to Change the email address or phone number for your Microsoft account to change your email address.
To launch an inPrivate browser window, see reference on Browse InPrivate in Microsoft Edge.
To check the expiration date, see Find out when your Microsoft 365 subscription expires - Office Support.
And the support can be accessed via contact support.
For more info, since we're Office 365 online support for business subscriptions, please post an additional thread under the category of Outlook.com or Microsoft 365 and Office / Account, billing and sign in / Other/unknown / Microsoft 365 Family.
B.
However, if you're using Microsoft 365 for Business/Enterprise, please note that only the admins can create a service request either via Online support or Phone support. See Get support | Microsoft Docs.
Hope it helps! If any update, welcome to share with us.
Also for your reference:
Thanks & Stay safe,
Qian