I called Singtel to ask about the free Priority Plus plan tryout. Those who have existing services with them, the charge in the bill will become credit for the upcoming bills.
Those who do not will have to call in and get the credit refunded.
Yea I called in to confirm too, Singtel's helpful CSO (from bill department, not just general helpdesk) explained to me the following.
There is no need for the trial customer to pay ANYTHING for the Singtel trial, even if the bill is already generated and there are supposedly incurred charges stated for the trial plan. You can just totally ignore the charges for the trial plan (please do however pay for whatever other lines/services you have with Singtel, as per normal).
How it works is that -
Singtel will generate your very next upcoming bill such that there will be a credit of exactly X amount to your account, so that the X amount of fees (generated from most recent bill) and X amount of credit (to be generated from upcoming bill) meant for the trial plan will cancel itself out. Thus, you don't need to pay anything in the end for the trial.
Singtel also confirms that ignoring the trial plan charges won't affect anything, including your other ongoing lines/services with Singtel if you have any.
Just to share all the above, if it helps anyone here understand the charges/bill for the trial plan better.