Service tax : applied in non assessee category. urgent help

Dear Sir,
We are a Labour & Construction society providing man power supply services. We have applied in "Non Assessee" category and deposited service tax in "non assessee" category up to september 2011. Because of non assesee category we were not able to file service tax returns. Thereafter w.e.f. october,2011 we applied a new service tax number and deposited service tax in new number. Now we are in receipt of a case against us regarding evasion of service tax. please tell me how to get credit of service tax deposited under non assessee category

Thanks & Regards
Nitin Garg