Service tax

I am a civil engineering and running a proprietorship form. i am doing civil works in industrial company on work contract basis. I have one service tax consultant past one year. i will gave him the service tax amount for return filing around 4.5 lakhs and always he said everything clear. but recently i have received one call from service tax department and they asked me why are you not filing return from the beginning. really i was shocked then immediately i try call consultant person his phone switch off.what i do,past one month i am unable to find that person. please give me a any remedy in my critical situation.