Input of service tax is claimed on payment or bill basis?

This query is : Resolved

Querist : Anonymous

Querist : Anonymous (Querist)

15 February 2016 I receive 10 bills from Airtel for mobile & internet charges on monthly basis for my employees. Along with the bill amount Airtel also charge extra 100 Rs for extra charges. After adding service amount & Rs 100 airtel charges service tax 14% + SBC 0.5%. but my Co. pays total bills amount except extra 100 Rs. like this Airtel bill.
Monthly charges 2000/-
Internet Charges 1500/-
Extra Rs added 100/-
taxable service 3600.00
+ Ser+Sbc 14.5% 522
Total bill Value as per airtel bill : 4122/-
My Co. Pays the bill amount excluding Rs 100/-. In this case as per payment basis service tax calculation would be changed. I want to know input of service tax credit would be taken as per bill basis or as per payment basis?