One word: Ask.
There were some errors in my billing and they told me my contract was over, and thus it’s back to the usual price. I asked to re-contract, but was only offered a 20% discount. The brochure I received in the mail a month before had a 50% offer, and so I pointed that out to him. After being put on hold for awhile, he came back, and in short, I got the 50% discount.
So if you are re-contracting your Broadband on Mobile with Singtel, try asking about the 50% discount promo.