Real estate gst impact on unsold underconstruction projects

The real estate industry has to comply with the new RERA rules as well as GST changes. 

Ours is an under construction project with half the units unsold . We have a huge amount of service tax deposited with the government. But since half the units are unsold and service tax is no longer a part of the regime from July we cannot collect service tax from customers .

1) will we be able to charge the customer gst and adjust it againsg the service tax deposited from July 1st . Otherwise we suffer a huge loss

2) if there are any units sold before July can we adjust the service tax collected on the instalment against the government deposit ?

thanks !