GST on Sub Sale Transaction

I am asking on behalf of my company. Recently we bought 9 units of Service Apartment which are being used as a hotel. On the title itself, there is restriction of interest whereas the building is for commercial purpose only. We had signed Sale & Purchase Agreement in 2014 and paid 10% Deposit.

Now, in March 2015, we have to pay Balance Purchase Price. The Sale & Purchase Agreement will be completed in the middle of May. We had received call from our Solicitor in charge for the sale and purchase transaction informed us that we will be charged 6% GST on payment of Balance Purchase Price if we pay in April 2015.

So I would like to know is it true or not? 6% GST chargeable from the total amount of Purchase Price. Can anyone explain to me regarding this matter? Thank you.