突然发现税单上面多了20%rebate

http://www.iras.gov.sg/irasHome/page04.aspx?id=14572
For the Year of Assessment 2013, all　tax residents　will　receive　an income tax rebate of up to $1,500.　You do not need to apply for this rebate as IRAS will compute this rebate automatically for all tax residents.　　
The tax rebate is based on the age of individual taxpayer. Details as follows:

Age as at 31 December 2012 Tax rebate Capped at　 Below 60 30% $1,500 60 and above　 50% $1,500