MR.A, CA raised an invoice for 27575 to a client on 20.06.11 . The lcinet, however, hs paid a lumpsum 26000 on 28.10.11 for full and final settlemtn. How much service tax Mr.A has to pya and when does this tax become due for payment ? what will be his liability, if the client refuses to apy service tax and pays only 25000 in total