Additional settings-related features and issues within Microsoft Teams Free
The only place where you can use your remaining Skype Credit to make phone calls is the Skype Dial Pad site on the Web:
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.
In the case your credit is deactivated due to not being used within the last 180 days, this credit can always be reactivated using this reactivation site: