If you or a Family Sharing member has a subscribed to the item or had a free trial to the item previously, you get charged immediately. It should state that on the Get button. You don't get multiple free trials or a trial after you have already been using an app.
How you get a refund depend upon through whom you subscribed. If Microsoft directly, go to their web site and find out how to do it there. Here's how to request an app or media refund from Apple (From: Request a refund for apps or content that you bought from Apple - Apple Support - see the article for more detail.)
1. Sign in to https://reportaproblem.apple.com
2. Tap or click "I'd like to," then choose "Request a refund."
3. Choose the reason why you want a refund, then choose Next.
4. Choose the app, subscription, or other item, then choose Submit.
If you were charged for a subscription that you no longer want, you can also cancel the subscription using the directions in this article --> If you want to cancel a subscription from Apple - Apple Support
Read this support article for information about how long it takes to receive a refund (if you are granted one), and how to check the status of a refund for apps or content that you bought from Apple --> Check the status of a refund for apps or content that you bought from Apple - Apple Support
Refs:
- Legal - Apple Media Services - Apple Section I
- Posts by Apple Communities contributor “Mac Jim ID” at Charged after cancelling free trial subsc… - Apple Community and Receiving a call transcript from phone su… - Apple Community
- Apple Support Article: If you want to cancel a subscription from Apple - Apple Support
