Point of taxation in case of security services.

We have received security services in the month of December 2012 of Rs. 1,50,000. We made advance payment of Rs. 75000 in the month of dec 12 & pay tax on the same on 05-01-2013. Bill Received in the month of 31st March 13 (i.e. after 30 days of completion of service.). Now what is Point of Taxation in this Case, Is it 31st December 2012 or 31st march 2013?