Have you clicked the link and try to subscribe? Usually it will work. Who do you talk to?
Singtel got different channels (Web, Facebook, Singtel Shop, 1688, WhatsApp, Roadshow, etc) and they kind of compete with each other. So do not listen to what they tell you, just click the link and see how it goes.
https://www.singtel.com/personal/products-services/mobile/eform/simonlyoffers
SIM Only Plus plan
12-month contract
150GB of data
FREE 8GB ReadyRoam Neighbours
1,000mins Talktime
500 SMS
FREE 12 months of 5G access
$20.37/mth