In Technical terms CC means Commencement Certificate and not completion certificate. YES, builder HAS to charge Service tax and VAT for flats sold even before or after obtaining CC. once the building is complete, government issues OC which means Occupancy Certificate, and flats sold / registered after that are free of Service tax and VAT.
No, he cann't charge VAT & Service after getting Completion Certificate. A property is termed under construction till the builder receives a completion certificate from the relevant authorities. If the entire amount for the property purchase is paid after the receipt of a completion certificate, there would be no service tax levied on the purchase of the property.