Yes, you can refund a credit package if it has been partially used. The customer will not be provided with a pro-rated refund, rather, the total cost of the credit package will be refunded back to the customer. All unused credits in the refunded credit package will automatically expire.
For example, a customer purchases a 10-pack for $250 and requests a refund after they have used 2 of the 10 credits. If you refund the credit package, the remaining 8 credits will expire immediately and the customer will be returned the entire $250.
If you want to see the option to give pro-rated refunds in the future, please submit the idea on our Product Roadmap.