QUOTE(dayamin @ Oct 7 2019, 08:30 PM)
Not sure about reducing balance .
But for my understanding is that (see below)
You overpaid RM33
in your celcom should show -RM33

Then RM499 with reducing balance = RM466
so you are required to pay RM466 for the penalty fee
reducing balance is a accounting term.
every asset depreciates in value over time. given enough time, it will be of no value to its owner.
your laptop may have a lifespan of 5 years before you throw it away. and your phone with sealed battery, probably have 3 years max before being outdated and no replacement parts to continue.
in this case, we can assume the celcom modem will have zero value to celcom after, say, 2 years.
we can have straight line depreciation, i.e. every month the modem will shed [RM499/24] until it reaches RM0 value after 24 months.
that RM33 above is overpayment as at that point in time. its effect is only after the total amount due is tabulated. e.g. your total penalty and what else will be RMxyz but you only need to pay [RMxyz-RM33] because you have paid that RM33 in advance.
disclaimer:
i didn't check if celcom really did mention reducing balance, and i simply plug in 24mth as the general contract lock-in.