Property tax tamilnadu

If the addition to the existing tax is based on false information,  you may send a representation to the commissioner of the city corporation giving details and seek his intervention or  to probe into the alleged false information and request to revise the tax as per earlier taxes. 

If you don't get a proper response or no respite then you can file an appeal against the order before taxation appellate tribunal for relief and remedy. 

Show the notice to a local prudent lawyer and challange it with concerned authorities / jurisdictional court

Is it that there is a "Head Room"?

To clear some points

• I have not received any Tax Revision Notice either hard copy or in corporation website.
• I am able to see the tax amount when i login with my mobile number in Chennai Corporation Website. Also getting SMS from corp to clear the taxes else there will be 1% penalty according to TNULB amendment act.
• There is no headroom the way to terrace he must have mentioned wrongly as headroom.

You can make appeal/representation to the higher authorities and if need be,  approach the judicial forums against the unfair enchancement of property tax.

If your representation to the corporation commissioner fails to fetch desired relief,  you were advised to approach taxation appellate tribunal where you can get justice as per law.