Builder is asking for Service Tax on flat purchased

Hi All, I indeed need help of all the experts registered on this site in my case as below, I have booked a under construction flat on 26th January-2010 and at the time of booking builder has confirmed that the registration of flat will be done in next 15 days. After that my real trouble started because whenever i have called the builder he kept me promising that it will happen in next 15 days. And at last the day came at the start of this month when builder has confirmed that Registrations are actually started. I took some time till today to arrange for the money of Stamp Duty and registration. Today when i called the builder for registartion details , then he has mentioned about the Service Tax Charges i have to pay by the mode of DD in his fafour. Please help me in geeting out of this fix, as i have booked property in January-2010 at that time the service tax was not applicable but because of builders delay i have to face the problem. is there any wayout by which i dont have to pay service tax on my flat purchase?