Service provided taxable when received is exempt

Seems to be a debatable matter . I feel that  liability arises because service has been provided and invoice has been raised prior to 01-05-2011. Hence as per new point of taxation rule taxable evet occurred.

when the servikce tax on medical services got disc ountinued, the service provider had to issue credit notes for st charged on overdue bills, in absence st so collected should be deposited to department.