12 July 2013
In case the bills raised by you is after 1.6.2010 it is not material whether the client has not paid you the service tax it is you who is to pay the ST. If it is before then as and when it is received you can pay it.
You are silent on the matter whether you have received the payment against your bill without the service tax then you can write to your client with a copy to the Commissioner ST. If your client says that the payment is inclusive of ST then you have to bear the ST from the Bill amount paid to you by your client.