it says there "follow you plan's validity"

it data booster add-on 2GB for RM3 to main plan. some booster valid for a few day, your bos is follow main plan.

you plan is monthly 1GB RM3/30 days validity auto renew. hey where u get this plan ? 12 month RM36 super-long-life

I think best2017 is 75 days. Need confirmation though.
RM1 to extend validity for 1 day. Upon expiry, you have 60 days or 75 days or 90 days grace ( depending on your plan) to buy again before line termination.
Prepaid Next is 90 days inactive grace period.

SMS is totally redundant on my Digi main line. The only time I send a SMS is to trigger the 90 days auto extension for my Unifi bebas numbers.
1) type *126# then add 90 days to your credit expiry date.
2) just follow the instructions I've posted earlier.
3) no.

1.The digi apps will show expiry date, u just add 90 days from expiry date, u also could use ussd *128# or *126#

2. In the app during 90 days grace period yr credit is frozen, but it allow u to buy 1 day validity to extend another 90 days grace period, u could buy 1 day validity in the app or dial *128#, so to speak to keep the digi prepaid alive, just set calendar reminder every 88days to buy rm1 1day validity.

3. The credit will remain before the line terminated, if u reactivate 1 day, yr credit still there with rm1 deducted.

All DiGi prepaid plans have 90 days grace period. When your credit validity expires, you will get an sms from DiGi that mentions:

Incoming calls until DD/MM/YYYY...

Treat that date as the termination date by which you need to top up or buy validity extension.

The MyDiGi app will continue to show the credit expiry date. Other telcos like Hotlink and Yes show the termination date, though not DiGi

As dgboy pointed out, all prepaid plan are now 90 days grace. App wouldn't show account termination date. You need to count the termination date yourself.