IMHO.Good point. SingTel hi! Postpaid plans inherited two things from Heya.
1) Base plan, 60 days validity with free incoming call
2) Rollover feature
Reference:
1) SingTel hi! 4G PostPaid plan terms and conditions
https://www.singtel.com/personal/products-services/mobile/hi/hi-terms-and-conditions
2) SingTel hi! 4G PostPaid plans FAQ
https://cdn1.singteldigital.com/con...ts-services/mobile/hi/pdf/singtel-hi-faqs.pdf
3) SingTel new Hi! App FAQ, for SingTel hi! 4G PostPaid plans
https://hi.singtel.com/faq
If it works, all these are not important.