Service tax on cancelled bill

dear sir

i am a commercial training and coaching service provider, during march 2012, i have raised an invoice with service tax @ 10.3% on the client and conducted the coaching. 

since mine is an advance billing, i have paid the service tax for this invoice on or before 31st march 2012 to the ST dept., and filed the respective half yearly st3 return.

during June 12, after long process, the client refused to pay even a single rupee on the bill raised for march 2012.

hence during june 12, (during F.Y 2012-13), i have reversed the bill and while paying service tax for the quarter, i have deducted the cancelled bill service tax amount from the quarter actual service tax amount payable.

please note, wef 1.4.12 i am charging 12.36% on the bills.

Now i have to file ST-3 half yearly return for the quarter april to june 12 as per new ST3, how i have to show the reduced service tax amount for the cancelled bill.  Since the cancelled bill is at old rate (10.30%)

First of all, am i eligible do such reversal, because my claim is genuine.

awaiting your expert commentry please