if the appointment that was purchased with the package credits is then cancelled the credits are not returned to the client's balance by default. To get the service reverted to the package limit of a particular client automatically you can go to Custom features -> Packages and enable "Automatically refund a package credit when a booking is cancelled" option.
if you relate the package with the recurring service and the client uses the package during the checkout process - currently 1 package credit is used for the whole pack of recurring sessions.