Service tax on advances

I have a Question on advances?? Suppose Mr X has Purchased a Flat which is under construction from a Construction Company Say ABC Pvt Ltd and Paid a Rs. 1000000/- as advance to the company as booking Amt. Total amount of Flat (Rs. 5000000). Now the Company has paid Service tax on this Amount as POT rules Falls when advance Recevied on Rs. 1000000. But Mr X has Paid the Balance amount of Rs. 4000000 after Completion of Construction of Flat, My question is that the Company ABC Pvt Ltd is required to pay service tax on Rs. 40 Lakh which is recevied by company after Completion of construction. (further it comes under defination of service or not as sale of immovable property)