Service Tax shown wrongly on bill.

Suppose a  proprietorship is providing painting work to its clients.

let us assume, it has provided service and gave Rs.100 bill to a pvt ltd. company(on the bill it is being written that Rs.8 is share of service receiver and Rs.4 is the share of service provider)

that pvt ltd. company paid THEIR share of service tax to govt.i.e. Rs.8 and then paid the bill amount of Rs.104 (Rs.100 bill value+ Rs.4 as proprietorship's service tax share) to the proprietorship firm.

turnover of proprietorship for any FY has not exceeded 9 lacs.

Now, question is, is the proprietoship firm required to get itself registered under service tax and pay its share of service tax to govt as appearing above i.e. Rs.4 ?

Please advise.

thnx.