Service provide to SEZ

Dear friends

We are providing service to a SEZ unit and charged service tax seperatly in bill raised by us. But we have not paid any service tax on this payment becaue we have not recived any payment yet. As per my knowledge we are not liable to pay service tax on this service.

Q Can we charged service tax on this service?

Q if we recive full payment with service tax than what?

Q Can we revice our bill and remove service tax on this payment.

Plz reply on urgent basis.

thanks in advance