Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
When Skype was discontinued last year, it was made clear that remaining credits are not refundable, but MIcrosoft still provides a way for users to use up the credits aia the Skype Web Portal:
https://calling.web.skype.com (Web portal will stay after Skype app goes away).
It might want you to reactivate your credits if you haven't used it at all during the last 180 days. Just follow the link it gives you to do so, or use this instruction
https://support.microsoft.com/en-us/skype/how-do-i-reactivate-skype-credit