Service tax

In the financial 2010-11 there were certain services on which service tax was payble on reciept basis,in one case assessee raised bill of Rs 10000/- and was included in the return as bill raised, In the next half year payment recieved after discount of Rs 2500/- which was not there in original invoice . what shoud be done in service tax return.

time period to revice return has been expired

Invoice should olso to be revised or not