Service tax on gta reverse charge

manish (sr manager finance & accounts)   (27 Points)

30 March 2016  
Dear all WE are mfg unit, for freight outwards & inwards we hired / contract with various transporters. Some transporters chrgd ser tax in their invoice and some transporters giving bills without ser tax. We are paying ser tax[GTA} those who not chrgd in the bill and taking cenvat credit. Some Excise authorities saying we have to pay all ser tax on behalf of transporters. Transporters no need to pay. Is it ok? Ser tax part on service receiver is optional or compulsory? Pl share ur views