Over charging in name of service charge

Location/place: Bangalore

Name of company/service: BJN Hotels

I went to Samarkand restaurant in Bangalore operated by BJN Hotels.They charged 10% service charge on total bill amount of food values instead of 40% of the food bill value.And despite of asking them about correction in bill,they insisted that it is correct.Following is the bill summary:
Food Bill value – 1695
Service Tax – 92.3
Service charge – 169.5
VAT – 270.36
Where as service charge should be 12.36% of 40% of 1695 which is 83.8 instead of 169.5 what they charged.
TIN number – 29210083947
CST – 0056245 dated 28-April-1998