The customer canceled the subscription, cancellation order was generated, but for zero sum - no refund was given to the customer.
The subscription period in the corresponding service plan is configured this way.
If you need to provide the refund to the customers on the subscription cancellation, change the settings:
Home> Product Director> Plan Manager> Service Plans> # Plan the subscription is based on Subscription Periods
choose the needed period, change After Refund Period from No Refund to Refund Prorated Recurring Fee.