Service tax on cancelled contracts

Respected All,

One of my client has received advance for booking of a flat and collect servive tax on the same & deposited to the central government. But later on, contract were cancelled and booking amount along with ST had been refunded.

Whether assessee can set off ST against future liablity or can claim for refund?

Please provide your valuable suggestion alongwith procedure.

Thanks & Regards,

Ramesh Purbia