Rules for Refunds

If the advertiser suspends or cancels their ad, then there is no refund.
The space remains reserved while the clock continues to run on the ad buy.

The space becomes available again.

If the publisher suspends or cancels the ad:
A publisher may suspend an ad for a maximum for 72 hours to give the advertiser time to make adjustment, however the clock continues to run. After the 72 hours, the ad is cancelled with cancellation rules applying.
An advertiser may suspend their ad to receive extra time to make changes and the advertiser suspension rule would apply.

A refund of the full amount of the ad buy is credited to the advertiser and debited from the publisher.
When the ad is cancelled, that space becomes available again.