Service tax payable with sales TAX TDS

Hello! I am a Railway Cntractor and registered as Contractor in CoT in Sales TAX. Iam Carrying out an AMC of some Telecom Asset, My query is while billing is done by Railways, say Rs.1,00,000/- Rlys. is deducting 4% of sales TAX and then Iam liable to pay service tax on Rs.1,00,000/-. Now here the value of sale is very less, though 4% is deducted in a AMC. In othe work contracts it is deducted it is justified, My query is how should i claim the excess sales TAX deducted in AMC while paying service tax (Difficult I feel as ST is a Central subject and Sales TaX is State Subject) Is there any notification for Non deduction of Sales tax in case of AMC or similar services where service and sales both are involved. Seniors Kindly guide me through this complication. ThanX, regards.