Service tax amount was deducted from my invoice amount

I have given man power service to X company for Amount:- 100000/-. I have given invoice amount :- 100000/-. (I don't having service tax registration) I not charged service tax on my invoice amount. But X company has deducted service tax amount from Invoice amt :- 100000 -15000 = 85000. They given payment only :- 76,500/- only (8500 - TDS). Please give suggestion what i have to do, to get my service tax amount