Service tax liability when taxes are due on different months

Hi

Please guide me on calculation of Service Tax Liability for the below case;

A Company charges Service Tax of Rs.1,40,000/- on a bill raised on 4/12/2014, but no input credits are available for this month. However in February and March 2015, it has paid service tax on input services as Rs.14,000 and Rs.42,000 respectively. It has not paid any service tax for the period. How to compute service tax liability and the interest as aplicable. I know i should take the rate at 18%p.a but not able to find out how to bifurcate the liability and take credit in the returns.

Thanks in advance.