Hi,
To get SLL (Super Long Life) validity options:-

You'll need to make sure your plan is:
1) DiGi New Best V1 or DiGi Best V4 (If you've activated DiGi Best plan before 1st of April.

Or

2) DiGi New Best V2 (Activated DiGi Best plan after 1st of April)

To check your plan:-
Dial *128*1*4# and call.

If you're on:
1) DiGi New Best V1 or DiGi Best V4 (365 days cost RM38)
2) DiGi New Best V2 (With Free Basic Internet, 365 days cost RM68)

To purchase Validity (SLL)
Dial *128*1*7*3# and call.