Real-time voice or video communication between users on mobile devices or computers
Unfortunately, unused Skype credit cannot be refunded. You can still use your available credit to make calls to phone number using the Skype Dial Pad site.
https://calling.web.skype.com/
Just be sure to sign in to this site with exactly the same account as you have used with Skype.
If you credit has been deactivated due to not being used without the last 180 days, then this credit can be reactivated from this site: