Unfortunately I have to say that that sort of puzzle requires help from "official" MS Support. They have access to the official documentation and (in theory) should be able to clarify your problem.
Do you have an annual or monthly subscription? If you are cancelling a yearly subscription before it renews there should not be a fee. Do you have a longer than one year subscription (somehow)?
I don't know anything about an "early termination fee" for cancelling a monthly subscription sounds like a scam, and an oxymoron.
The business faq < https://products.office.com/en-us/business/microsoft-office-365-frequently-asked-questions > says
this
<snip>
Can I cancel my subscription at any time?
You can cancel your subscription at any time. However, depending on the product and the type of subscription you have, there may be a penalty for canceling before the end of your contract. For subscriptions with a monthly commitment payment, there is no
penalty for canceling your contract at any time. Annual commitment subscriptions that are paid month to month may incur some penalties if canceled early. Annual commitment subscriptions that are paid up front do not receive a refund if canceled prior to the
full contract period. Read the complete Microsoft Online Subscription Agreement.
</snip>
Here is the process for cancelling a subscription (which I'm pretty sure you already know)
Immediate Cancel a Microsoft subscription / stop Auto Renew
http://windows.microsoft.com/en-us/windows-10/cancel-a-microsoft-subscription#v1h=tab01
Stop automatic renewal
Cancel immediately
To stop automatically renewing your subscription, but keep using it until it expires:
- services and subscriptions page with your Microsoft account.
- Cancel.
- Cancel at the end of the subscription period, then select
Next.
- Confirm cancellation.
- Note: If you have a pending balance, we’ll ask you to pay it when you cancel. If you don’t pay, we’ll charge your payment
option on the next billing date.
To cancel your subscription immediately, and lose access to the service:
- services and subscriptions page with your Microsoft account.
- Cancel.
- Next.
- Confirm cancellation.
- Note: If you have a pending balance, we’ll ask you to pay it when you cancel. If you don’t pay, we’ll charge your payment
option on the next billing date.