St and vat on semi-finished flat pruchase (real estate)

I purchased a flat in semifinished stage for 64.31lacs and builder has devided the sale consideration of 25.80 lacs towards sale deed and 38.51 lacs towards construction agreement and charging me service tax @ 4.5% on total sale consideration of 64.31 lacs and VAT @ 1.25% on Construction agreement value and service tax component. I understand from my peers that Service Tax is to be paid only on Construction Agreement value of 38.51 lacs only, not on total consideration of 64.31 lacs. I am endingup paying more towards service tax.Can anyone brief me on the rule position.