Service tax invoice date

A company raised a bill of twenty lacs in a month. service tax @ 14.5% of 20 lacs is two lacs ninty thousand. payments are coming after 3 months atleast. It means 2.9 lacs*3=8.7 lacs. This amount is creating pressure on the copany and resulting decrease in capital. if we are paying after payments which is after 3 months then service tax department is claiming interest which is again a pressure for no default by the company. This is the issue.