Service tax return-abatements

One of my client is providing work contract service and rent a cab service and taking benefit of abatements viz. 30% on WCR and 60% on Rent a cab but I am getting confused regarding their notification number and serial number and how to show amount bcoz service receiver's liability to pay under RCM @ 100% on 40% in rent a cab service and 50% on 70% of taxable amount in wcr while tax rate cannot be reduced just bcoz of system errors, so plz give me suggestions??? Thanks in advance