It seems that they update their T&C on their website:
https://www.sc.com/sg/promotion/2015/singpost/tnc.html
The following transactions are not considered eligible retail transactions for the purposes of this Promotion and will therefore not be taken into consideration towards the fulfilment of the Minimum Spend Criteria in Clause 2(b)(ii):
online bill payment from Standard Chartered Online Banking and/or Breeze Mobile Platform;
payments to the Immigration & Checkpoints Authority, the Ministry of Manpower, and income tax payments;
purchase and top-up of EZ-Link cards;
insurance premiums charged to the Eligible Card;
balance transfers to the Eligible Card, cash advances from the Eligible Card, purchases via NETS and ongoing instalment payments;
any fees and charges (including annual fees, interest charges, cheque processing fees, administrative fees, cash advance fees, finance charges and/or late payment charges and other miscellaneous fees and charges) charged to the Eligible Card;
balance owing on the Eligible Card account from other months.